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/tLFitED  w.  net. 


Digitized  by  the  Internet  Archive 

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http://www.archive.org/details/concretehouseitsOOsloaiala 


The  Concrete  House 

and  its 

Construction 


The  Concrete  House 

and 

Its  Construction 


By  Maurice  M.  Sloan 


Price,  $1.00 


Published  by 
The  Association  of  American 
Portland  Cement  Manufacturers 

Philadelphia,  1912 


Copyright,  1912,  by 
Association  of  American  Portland  Cement  Manufacturers 


PRESS  OF  WM.  F.  FELL  COMPANY 
PHILADELPHIA 


Preface 

The  demand  for  fire-resisting,  durable  and  sanitary  construction  has  been 
the  dominant  note  in  most  that  has  been  said  and  written  on  the  subject 
of  architecture  during  the  last  decade.  The  American  dwelling  of  the 
best  class  is  a  model  of  convenience,  comfort  and  beauty,  and  these 
attributes  may  be  found  even  in  houses  of  moderate  cost.  But  with  rare 
exceptions,  three  fatal  defects  accompany  modern  construction.  Modern 
houses  are  not  fire-resisting,  not  durable  and,  to  a  lesser  degree,  not 
sanitary. 

Knowledge  of  these  facts,  coupled  with  that  newly  awakened,  ir- 
resistible demand  for  vastly  increased  economy  and  efficiency  in  the 
nation's  industrial  and  social  development,  has  led  American  architects 
to  concentrate  every  effort  toward  the  solution  of  the  problem.  They 
found  that  the  highest  standard  of  fire-resisting  construction  was  so 
closely  allied  with  extreme  durability  and  sanitary  excellence  as  to  em- 
brace these  three  important  structural  reforms  under  that  single  head. 
Iron  and  steel  did  not,  unless  protected,  represent  fire-resisting  construc- 
tion, and  in  this  investigation  many  other  materials  were  rejected  as  non- 
fireproof  in  themselves. 

In  the  average  house,  fire  starting  in  the  cellar  soon  transforms  the 
building  into  a  smoking  ruin.  Only  the  eternal  vigilance  of  our  fire 
departments,  maintained  at  a  cost  of  more  than  $100,000,000  annually, 
prevents  the  destruction  of  thousands  of  homes  each  year. 

A  study  of  the  fire  losses  of  this  and  European  countries  shows  our 
annual  loss  to  be  $2.51  per  capita,  while  in  the  cities  of  the  six  leading 
nations  of  Europe  it  is  only  33  cents. 

That  fire-proof  construction  is  the  exception  rather  than  the  rule, 
is  due  mainly  to  a  mistaken  idea  of  its  cost.     Fire-resisting  floors  and 

[5] 


roofs  are  not  prohibitive  in  cost,  and  even  though  the  architect  be  wedded 
to  concrete,  brick  or  stone  in  the  matter  of  walls,  he  is  in  favor  of  fire- 
proof interior  construction. 

The  purpose  of  this  book  is  to  make  clear  the  advantages  of  concrete 
in  the  construction  of  dwellings. 

Experiment  and  research  have  reduced  the  list  of  available  fire- 
resisting  materials  to  practically  two  products — concrete  and  clay.  Con- 
crete is  not  only  a  superior  fire-resisting  material,  but  ranks  supreme  from 
the  standpoint  of  economy,  owing  to  the  facility  with  which  it  may  be  used 
for  practically  every  structural  detail  of  a  house.  Its  wide  range  of  adapta- 
bility has  been  demonstrated  by  such  architects  as  McKim,  Mead  & 
White,  who  used  concrete  with  distinguished  success  in  the  new  Pennsyl- 
vania Terminal  Station,  in  New  York  city,  where  it  is  usually  mis- 
taken for  costly  stone  work.  Carrere  &  Hastings  chose  simple  concrete 
blocks  for  the  costly  Steers  mansion,  near  Greenwich,  Conn.  Mr.  Gros- 
venor  Atterbury,  in  charge  of  the  Sage  Foundation  work,  achieved  re- 
markable results  with  concrete  in  seeking  to  better  the  living  conditions 
of  the  laboring  classes  by  his  invention  of  cheap  houses  of  solid  and  seam- 
less concrete,  a  type  more  durable,  sanitary  and  fire-resisting  than  the 
majority  of  our  most  costly  dwellings. 

In  work  of  this  kind,  as  well  as  in  great  engineering  achievements, 
is  to  be  found  indisputable  evidence  that  the  restricted  use  of  concrete 
in  the  construction  of  dwellings  is  not  due  to  any  defect  or  limitation 
of  the  material  itself,  but  chiefly  because  architects  have  failed  to  give 
the  subject  the  serious  consideration  it  deserves.  The  fact  that  concrete 
is  a  comparatively  new  material  has  also  had  a  retarding  influence,  but 
now  that  striking  examples  of  its  extreme  utility  as  well  as  perfect 
adaptability  to  artistic  expression  are  to  be  found  in  many  sections  of  the 
country,  there  is  promise  that  concrete  houses  will  become  the  rule 
rather  than  the  exception. 

This  book  does  not  treat  of  the  subject  in  a  superficial  way,  but  goes 
into  all  the  details  of  concrete  construction  as  applied  to  houses,  and  it 
is  published  with  the  conviction  that  it  will  have  a  real  and  practical 
value  to  the  architect. 

[6] 


McKim,  Mead  and  White,  Architects 


Pennsylvania  Terminal  Station,  New  York 

Above  the  costly  Travertine  stone,  imported  from  Italy,  the  interior  walls 
are  faced  with  concrete,  colored  and  cast  in  imitation  of  this  stone.  Even 
experts  have  been  deceived  as  to  the  point  where  the  stone  ends  and  the  con- 
crete begins.  The  economy  and  utility  of  concrete  for  architectural  purposes 
is  strikingly  exemplified  in  this  magnificent  building. 


Chapter  I 

The  Advantages  of  Concrete  for 
House  Construction 


Chapter  I 
The  Advantages  of  Concrete  for  House  Construction 

Fireproof  Qualities  of  Concrete. — It  would  be  difficult  to  plan  and  con- 
struct a  house  that  would  ignite  quicker  or  burn  faster  than  the  common 
type  of  dwelling.  Every  architect  and  builder  understands  the  danger 
of  studded  partitions,  wooden  floor  joist  and  outside  sheathing,  the  close 
proximity  of  timber  construction  to  chimneys  and  flues,  the  inaccessible 
recesses  of  the  hollow  frames  into  which  chips  and  shavings  have  fallen, 
the  knob  and  tube  work  of  electric  wiring.  To  mention  these  features 
of  the  ordinary  house  brings  realization  of  the  constant  peril  confronting 
those  obliged  to  live  in  them. 

The  antithesis  of  all  this  is  found  in  concrete.  Concrete  means  fire- 
proof walls  and  floors  at  very  little  cost  in  excess  of  combustible  con- 
struction. Floors  of  concrete  are  non-combustible.  Moreover,  they 
will  confine  smoke  and  flames  to  the  room  in  which  a  fire  may  start. 
They  practically  eliminate  the  danger  of  suffocation  from  smoke,  so 
often  followed  by  loss  of  life.  Concrete  not  only  affords  a  sense  of  se- 
curity in  this  respect,  but  so  far  as  the  building  itself  is  concerned  makes 
insurance  unnecessary.  There  is  no  instance  on  record  where  a  build- 
ing constructed  of  reinforced  concrete  throughout  has  been  destroyed 
by  fire  or  conflagration. 

In  tests  of  concrete  panels  conducted  by  the  U.  S.  Geological  Sur- 
vey, a  heat  of  17000  Fahr.  was  maintained  for  two  hours.  At  the  expira- 
tion of  that  time  paper  labels  on  the  backs  of  the  specimens  were  not  even 
scorched  and  the  concrete  could  be  touched  by  the  hand  without  dis- 
comfort. Professor  Ira  H.  Woolson,  formerly  of  Columbia  University, 
now  Consulting  Engineer  of  the  National  Board  of  Fire  Underwriters, 

[11] 


used  as  a  test-house  a  structure  with  four-inch  walls  of  cinder  concrete 
which,  according  to  the  last  report,  was  intact  after  tests  aggregating 
twenty  hours.  The  temperature  ranged  from  17000  to  19000  Fahr.,  which 
is  in  excess  of  estimated  conflagration  temperatures.  Moreover,  at 
the  end  of  each  four-hour  test,  and  while  the  walls  were  red  hot,  a  stream 
of  water  at  60  pounds  nozzle  pressure  was  played  back  and  forth  over  the 
ceiling  for  ten  minutes — a  terrific  punishment — but  the  walls  remained 
intact.  All  this  is  far  in  excess  of  anything  buildings  encounter  in  ordi- 
nary fires.  In  a  word,  in  the  true  concrete  house,  lamps  might  explode, 
furnaces  melt  of  their  own  heat,  wires  become  crossed  and  flues  over- 
heated, or  any  of  the  hundred  and  one  accidents  occur  that  cause  fires, 
without  the  slightest  danger  to  the  building.  Only  the  contents  could  be 
destroyed.  Many  owners  of  concrete  buildings  carry  no  insurance  on 
the  structures. 

In  every  large  city  of  a  million  or  more  inhabitants,  from  five  to 
ten  fires  start  each  day.  Some  days  the  list  is  greatly  in  excess  of  this 
number.  They  are  never  noted  by  the  public  unless  of  the  spectacular 
kind,  involving  great  loss  of  life  or  property,  or  attended  with  dramatic 
features.  But  were  it  not  for  the  ever-vigilant  fire  departments,  each 
one  of  these  incipient  fires  might  easily  cause  a  conflagration.  It  costs 
the  country  one  hundred  millions  a  year  just  to  extinguish  such  fires. 
Our  total  loss  from  fire  is  $450,000,000  annually.  In  nearly  every  in- 
stance the  damage  is  caused  by  the  use  of  combustible  material  in  build- 
ing construction.     Concrete  is  non-combustible. 

Durability. — As  to  the  stability  or  strength  of  a  concrete  house,  the 
following  is  an  example  strikingly  typical:  Preceding  the  recent  earth- 
quake in  Jamaica,  there  was  a  scarcity  of  water,  and  at  the  concrete 
residence  of  Mr.  Alfred  Mitchell,  in  Port  Antonio,  bath-tubs  were  used 
as  temporary  tanks  or  reservoirs.  During  the  earthquake  this  house  was 
rocked  until  the  water  splashed  over  the  sides  of  the  tubs.  Mr.  Mitchell, 
whose  American  residence  is  New  London,  Connecticut,  wrote  that  the 
house  had  passed  through  the  ordeal  without  showing  the  least  crack. 
Other  buildings  in  the  district  were  utterly  demolished.     This  remark- 

[12] 


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able  strength  may  be  obtained  in  the  small  and  cheap  concrete  dwelling 
as  readily  as  in  a  large  and  costly  house.  In  this  matter  of  durability 
we  again  encounter  in  concrete  the  very  opposite  of  other  materials.  It 
improves  with  age.  Its  known  life  runs  into  thousands  of  years.  Wood 
shrinks,  warps,  burns  and  decays;  stone  and  brick  units  fall  apart  and 
are  disrupted  through  the  action  of  frost  and  temperature  changes.  Con- 
crete is  improved  both  in  quality  and  appearance  by  exposure  to  the 
weather.  It  may  be  used  for  foundations,  walls,  floors,  roofs,  stairways 
and  chimneys,  thus  making  a  solid,  seamless  house  throughout. 

Vermin-Proof  Qualities. — With  concrete  it  is  possible  to  so  build 
walls  and  floors  as  to  make  them  impervious  to  rats,  mice  and  other  ver- 
min, too  often  the  purveyors  of  disease.  In  a  word,  concrete  houses  may 
be  made  as  sanitary  as  they  are  fire-resisting.  Concrete  floors  and  walls 
tend  to  prevent  either  the  admission  or  accumulation  of  things  dangerous 
to  health,  many  of  which  find  protected  habitat  in  the  recesses  of  the 
ordinary  house. 

Non-Conductivity  of  Concrete. — The  low  conductivity  of  concrete, 
which  makes  it  such  an  admirable  fire-resisting  material,  also  retards  the 
entrance  of  cold.  When  properly  made  it  is  devoid  of  cracks  and  im- 
perfect joinings.  Settlement  of  walls,  so  common  in  buildings  of 
brick  and  stone,  is  not  apt  to  occur.  It  is  not  a  paradox  to  say  that  the 
concrete  house  is  cool  in  summer  and  warm  in  winter.  It  has  been 
found  by  actual  experiment  that  a  saving  of  20  per  cent,  in  the  cost  of 
fuel  has  been  obtained  by  substituting  concrete  for  brick,  stone  or  frame. 
In  the  concrete  house  shown  in  Fig.  14  the  temperature  is  15  degrees 
lower  than  the  outside  temperature  on  the  hottest  days  of  summer. 

Sound-Proof  Qualities  of  Concrete.— Concrete  possesses  marked 
sound-proof  qualities.  When  concrete  is  used  throughout  a  dwelling  there 
results  a  minimum  of  sound  transmission,  insuring  the  quiet  and  repose  so 
essential  to  the  ideal  home.  Allied  to  this  is  the  exceedingly  desirable 
attribute  of  rigidity,  which  in  turn  means  non-vibrating  floors.     The 

[15] 


virtue  of  concrete  in  this  respect  is  so  pronounced  that  in  factory  con- 
struction it  has  come  to  be  regarded  as  an  economic  factor  of  the  highest 
importance,  making  for  increased  efficiency  as  well  as  representing  a 
material  saving  in  the  wear  and  tear  of  machinery. 

Low  Cost  of  Upkeep. — As  stated,  concrete  means  the  elimination  of 
insurance  on  the  building  and  the  same  thing  applies  to  the  cost  of  up- 
keep or  repairs.  For  this  reason  it  is  highly  important  to  determine 
whether  the  cheapest  construction  is  not,  after  all,  the  most  expensive. 
At  the  expiration  of  seven  or  eight  years,  repairs  become  an  important 
item  in  the  case  of  the  average  house,  and  this  should  be  carefully  esti- 
mated when  the  first  cost  is  considered.  If  the  value  of  property  is  to 
be  maintained  it  must  be  kept  in  first-class  condition  and  in  the  case  of 
ordinary  construction  this  can  only  be  done  through  constant  repairs. 

Walls  of  concrete,  especially  when  solid  and  untreated  as  to  surface 
finish,  require  absolutely  no  repairs,  and  when  floors  and  roofs  are  con- 
structed of  the  same  material  the  up-keep  would  be  confined  merely 
to  the  painting  of  windows  and  doors.  The  prevailing  notion  that  the 
cost  of  a  concrete  house  is  far  in  excess  of  other  materials  is  absolutely 
wrong.  The  partial  imitation  of  other  houses  in  concrete— that  is  to  say, 
a  house  with  concrete  walls — may  exceed  slightly  the  cost  of  other  types, 
but  it  has  frequently  happened,  especially  where  sand  and  stone  were 
convenient,  that  the  cost  was  less.  But  in  the  true  concrete  house, 
that  is  to  say,  a  house  of  concrete  throughout,  its  duplicate  in  stone  or 
brick  would  be  prohibitive  in  cost.  As  matters  stand  to-day,  there  is 
no  fair  basis  of  comparison,  for,  as  stated,  all  that  has  been  done  up  to 
date,  except  in  very  rare  cases,  has  been  to  build  the  usual  type  of  house 
with  concrete  walls.  The  trend  at  present,  however,  is  toward  the  ab- 
solutely fireproof  and  indestructible  house  that  shall  be  of  concrete  from 
foundation  to  roof.  The  same  type  of  house  in  brick  or  stone,  if  practic- 
able at  all,  would  cost  three  times  as  much  as  the  concrete  house.  It  is 
in  looking  at  the  concrete  house  from  this  point  of  view  that  we  begin 
to  comprehend  its  true  significance  and  value. 


i6l 


Chapter  II 

Architectural  Design  and  Treatment 
of  Concrete  Houses 


Chapter  II 
Architectural  Design  and  Treatment  of  Concrete  Houses 

The  fundamental  rule  of  all  good  architectural  design  is  that  the  ap- 
pearance of  the  building  shall  express  the  structural  capabilities  of  the 
materials  of  which  it  is  composed.  The  great  main  divisions  of  archi- 
tectural history  are  marked  either  by  the  adoption  of  new  materials  or 
by  improved  methods  of  using  the  old  ones.  But  as  all  transition  in 
architectural  styles  is  slow  and  gradual,  elements  of  previous  architectural 
design  still  appear  in  the  newer  styles.  So  it  is  that  the  columnar  halls 
of  the  Egyptian  temple  take  their  proportions  and  construction  from  the 
rock  temples  carved  in  the  mountain  side,  where  gigantic  pillars  were  left 
to  support  the  roof  of  the  vault,  as  in  modern  mine  workings. 

The  Greeks,  following  the  precedent  of  the  Egyptians,  built  with  the 
stone  column  and  superimposed  lintels  until  the  Romans  developed  the 
arch,  and  learned  that  great  spans  could  be  made  by  supporting  an  arch 
ring  of  stones  upon  heavy  buttresses.  It  remained,  however,  for  those 
masters  of  Gothic  architecture,  the  medievalists,  to  produce  a  new  archi- 
tecture by  balancing  arch  thrust  with  arch  thrust,  and  supporting  the 
whole  gigantic  and,  withal,  light  and  wonderful  structure  upon  isolated 
piers,  the  beauty  of  which  has  never  been  surpassed. 

The  Development  of  a  Particular  Style. — The  difference  thus  seen 
between  the  two  great  historical  divisions  of  architecture  is  based  on 
the  structural  design.  In  the  first  instance  the  elements  of  the  classic 
orders  are  the  lintel  and  the  column,  while  in  Gothic  architecture  the 
design  depends  upon  the  vault,  arch  and  buttress.     All  other  sub-divi- 

[19] 


sions  of  architectural  design  are  purely  adaptations  of  these,  and  illustrate 
either  growth  or  decadence. 

In  modern  times  new  materials  have  been  introduced.  The  use  of 
structural  steel  has  developed  designs  impossible  with  any  other  material ; 
but  even  with  this  modern  material  the  use  of  the  column  and  lintel  is 
adhered  to.  For  the  application  of  an  entirely  new  principle  in  construc- 
tion one  must  turn  to  reinforced  concrete.     This  differs  from  all  other 


Fig.  I. — A  false  or  strained  surface  treatment  representing  waste  of  time  and 

money. 


materials  heretofore  used  in  that  it  is  composite,  using  the  tensile  re- 
sistance of  steel  to  develop  the  compressive  resistance  of  a  monolithic 
artificial  stone,  and,  with  it  all,  possessing  a  quality  of  fireproofness be- 
yond that  of  any  material  previously  employed  for  building  purposes. 

If  particular  styles  of  architecture  can  be  developed  from  the  column, 
lintel  and  arch,  it  is  certain  that  in  the  use  of  a  new  material  such  as  re- 
inforced concrete,  a  style  of  architectural  design  and  decoration  can  be 

[20] 


developed  which  will  express  truly  the  nature  and  capabilities  of  the 
material.  Unfortunately,  it  is  difficult  to  overcome  the  habits  of  years 
and  the  training  of  past  generations,  so  that  up  to  the  present  time  the 
architectural  designer  has  shown,  in  handling  reinforced  concrete,  the 
influence  exerted  by  previously  used  materials. 

The  effort  of  the  architectural  designer  to  imitate  masonry  construc- 
tion in  handling  reinforced  concrete  is  very  evident  in  the  building  il- 
lustrated in  Fig.  i.  This  shows  an  effort  to  deceive  the  observer  into  a 
belief  that  the  structure  is  built  up  of  blocks  cemented  together,  and,  in 
order  to  make  the  deception  doubly  real,  the  joints  are  boldly  marked  by 
casting  a  bevel  into  the  concrete  to  illustrate  the  chambered  joints  of 
massive  masonry  construction.  Not  satisfied  with  this  effort  to  simulate 
masonry,  the  designer  sometimes  goes  to  the  extent  of  bush-hammering 
the  center  section  of  the  blocks,  after  the  manner  of  the  earliest  methods 
of  dressing  stone. 

In  the  design  of  dwelling  houses  the  user  of  concrete  first  employed 
hollow  concrete  blocks,  and  the  early  efforts  were  exerted  in  making  these 
blocks  look  like  rock-faced  ashlar.  Unfortunately,  all  of  the  molds  had 
the  same  pattern,  and  instead  of  getting  the  variations  of  light  and  shade 
which  make  up  the  life  of  rock-faced  stonework,  the  entire  building  be- 
came a  monotonous  repetition  of  units,  with  the  same  highlights  and 
shades. 

The  thoughtful  designer  who  is  about  to  use  concrete  as  a  struc- 
tural and  decorative  material  will  endeavor  to  determine  how  best  he  can 
use  the  peculiar  properties  of  concrete  and  reinforced  concrete  to  obtain 
a  true  expression  of  the  capabilities  of  the  material  and  at  the  same  time 
to  develop  a  structure  which  will  be  pleasing. 

The  essential  difference  in  the  possibility  of  reinforced  concrete,  as 
compared  with  the  lintel  and  column  supports  of  the  classic  orders  and 
the  vaulted  arch  and  buttress  of  the  later  medieval  construction,  is  that 
it  is  practically  a  masonry  material,  possessing,  besides  the  great  com- 
pressive resistance  of  stone,  the  tensile  strength  of  the  steel  which  can  be 
embedded  in  it.  It  is  therefore  possible  to  develop  a  particular  style  of 
architecture  in  working  in  this  material,  though  it  can  be  used  for  the 

[21] 


Fig.  2. — One-story  concrete  workingman's  cottage,  exemplifying  simple  and 
direct  use  of  concrete. 


Fig.  3. — A  carefully  studied  design,  showing  frank  treatment  of  concrete  walls 

and  surface  finish. 


development  of  almost  any  architectural  treatment,  a  feature  which  is 
particularly  valuable  in  house  construction. 

Architectural  Composition  of  Concrete  Houses. — The  use  of  con- 
crete in  monolithic  construction  for  dwelling  houses  has  been  some- 
what limited,  although  rapid  advance  is  being  made,  both  for  houses  of 
moderate  cost  and  pretentious  residences  of  great  cost. 


Fig.  4. 


-Buttressed  porch  construction  in  monolithic  concrete.     Impracticable 
in  other  types  of  masonry. 


To  illustrate  the  wide  range  that  concrete  has  already  reached  in 
dwelling  house  construction  reference  is  made  to  Figs.  2  and  3,  which 
show  an  interesting  comparison  with  reference  to  size  and  cost. 

In  Fig.  2  there  is  shown  a  one-story  concrete  cottage  erected  at 
Ada,  Oklahoma.  The  design  of  this  dwelling  would  probably  not  please 
the  aesthetic  taste  of  the  architectural  designer,  yet   one  cannot  help 

[23  1 


considering  how  superior  in  architectural  pretensions  this  small  dwelling 
is  in  comparison  to  its  prototype  built  of  wood,  replete  with  band-sawed 
brackets  and  fussy  wooden  finials  and  cornices,  so  familiar  two  decades 
ago  in  houses  of  equal  value.  Fig.  3,  on  the  other  hand,  shows  a  con- 
crete house  which  has  been  carefully  studied  by  a  skilled  architect,  and 
it  is  peculiarly  interesting  from  the  fact  that  the  actual  texture  of  the 
concrete  of  which  the  walls  are  composed  shows  in  the  illustration.  One 
of  the  excellencies  of  this  house  is  in  the  design  of  the  facade.  There  has 
been  a  very  evident  appreciation  of  the  character  of  the  material  in  that 
no  attempt  has  been  made  to  form  imitation  arches  over  the  heads  of 
the  openings.  The  nature  of  the  material  is  also  expressed  in  the  forma- 
tion of  the  gables,  both  at  the  peak  and  the  eave  line,  in  the  buttresses 
of  the  chimney,  corner  walls,  and  coping  and  buttresses  of  the  garden 
wall. 

One  might  dispute  the  statement  that  such  buttresses  as  illustrated 
in  Fig.  4,  which  shows  the  construction  of  a  porch  of  a  solid  concrete 
residence  built  in  Milwaukee,  are  expressive  of  reinforced  concrete  con- 
struction. They,  however,  are  certainly  monolithic  in  their  profile,  as 
it  would  be  extremely  difficult  and  impractical  to  build  such  buttresses 
in  masonry.  This  design  is  also  expressive  of  the  material  on  account  of 
the  formation  of  the  arched  openings,  which  would  be  impractical  in 
ordinary  masonry  construction.  The  drain  spouts  or  scuppers  from  the 
porch  are  an  ornamental  detail  indicative  of  the  material  when  used 
to  the  best  advantage. 

In  order  to  illustrate  a  few  of  the  structural  possibilities  of  reinforced 
concrete  with  reference  to  house  construction,  and  to  show  how  these 
possibilities  will  eventually  develop  a  new  style  of  house  architecture, 
attention  is  called  to  Figs.  5  and  6. 

In  Fig.  5  an  interesting  example  of  the  use  of  reinforced  concrete  is 
shown  in  the  projecting  porch  or  balcony  at  the  rear  of  the  building,  and 
the  detail  illustrates  the  possibilities  of  the  material  for  features  of  this 
character.  If  the  building  had  been  constructed  of  timber,  this  projecting 
porch  would  have  been  carried  on  unsightly  posts,  or  insecure  and  unen- 
during  wooden  brackets,  whereas  by  the  use  of  concrete  a  perfectly  safe 

[24I 


m£D  W.  RE  A. 


Fig.  5. — A  house  showing  the  adaptability  of  concrete  to  the  construction  of 
projecting  masonry. 


fc--:-^Bfc£:-- 


Fig.  6. — Concrete  as  adapted  to  the  requirements  of    English   half-timber 
design.     Note  monolithic  corbel  or  shelf  supporting  window. 

I  25] 


and  everlasting  construction  is  accomplished.  While  the  dwelling  here 
described  is  not  intended  to  be  presented  as  a  particularly  pleasing  de- 
sign, it  illustrates  very  well  the  use  of  concrete  in  wall  construction. 

To  further  show  the  practicability  of  reinforced  concrete  in  the  con- 
struction of  details  which  could  not  be  so  well  accomplished  by  other 
materials,  attention  is  called  to  Fig.  6,  and  is  particularly  directed  to  the 
manner  in  which  the  bay-window  on  the  side  is  supported  by  a  monolithic 
corbel  or  shelf.  It  also  shows  the  manner  in  which  reinforced  concrete 
walls  can  be  decorated  to  meet  the  requirements  of  the  English  half- 
timber  house  design.  All  of  the  walls  of  this  house  are  of  solid  concrete, 
the  surface  being  finished  by  bush-hammering. 

A  consistent  and  interesting  detail  is  also  shown  in  the  porch  and 
open  promenade  connected  with  the  house,  this  work  being  really  ex- 
cellently designed,  massive  and  simple,  and  altogether  pleasingly  ex- 
pressive of  the  capabilities  of  the  material. 

To  further  show  the  beginning  of  the  designer's  appreciation  of 
the  possibilities  of  solid  concrete  for  house  construction,  attention  is 
directed  to  Fig.  7.  It  shows  the  long  spans  possible  for  such  details  as 
porch  construction.  It  must  be  remembered  that  such  spans  are  ob- 
tained without  any  danger  of  settlement  due  to  deflection  or  the  shrink- 
age of  timber.  They  typify  the  material,  and  will  become,  as  the  archi- 
tectural designer  attains  skill  in  the  handling  of  the  material,  more  and 
more  prominent  in  reinforced  concrete  house  construction.  Again,  the 
peculiar  adaptation  of  the  material  in  forming  the  base  or  ledge  support 
for  the  bay  window  is  illustrated  in  this  example,  and  the  possibilities  of 
reinforced  concrete  are  also  shown  in  overhanging  pent-roofs  at  the  eave 
line.  These  are  unique  since  they  are  constructed  of  concrete,  which  is 
admirably  suited  to  the  purpose. 

The  illustration  which  is  the  subject  of  these  remarks  is  a  twelve- 
roomed  house  constructed  at  Winthrop,  Mass.  This  house  when  partially 
completed  was  instrumental  in  stopping  the  sweep  of  a  serious  conflagra- 
tion. At  the  time  of  the  fire  the  outside  walls  were  up  to  the  second 
story,  and  while  the  wood  window-frames  were  burned  away,  the  concrete 
was  not  damaged,  and  the  construction  was  resumed.     The  floors  of  this 

[26] 


dwelling  are  of  concrete  construction,  and  the  example  may  be  studied  for 
possibilities  in  the  design  of  concrete  dwellings  of  similar  size. 

Solid  concrete  construction  lends  itself  admirably  to  designs  in 
which  simplicity  predominates  both  in  plan  and  in  elevations.  Con- 
crete is  never  more  interesting  than  when  in  flat  wall  surfaces  it 
shows  to  advantage  the  proportion  and  placing  of  the  window  and  door 


illllll  llj  iffiji  J | 


•      mmm  - 


Fig.  7. — A  porch  illustrating  the  practicability  of  long  span  construction  in 

concrete. 

openings,  and  when  the  gray  walls  are  made  beautiful  and  interesting  by 
the  high  lights  and  shadows  of  a  bright  sunlight. 

An  example  of  the  consistent  use  of  concrete  in  house  construction  is 
illustrated  by  Fig.  8,  which  shows  a  concrete  house  of  the  utmost  sim- 
plicity; one  extremely  beautiful  in  this  quality.  A  study  of  the  per- 
spective shows  that  the  structure  is  entirely  devoid  of  appliqued  orna- 
mentation, and,  in  fact,  the  only  attempt  at  a  purely  architectural  orna- 

[27] 


mentation  is  found  in  the  molded  architrave  over  the  main  entrance 
doorway.  The  cornice  is  beautiful  because  it  expresses  the  material, 
and  no  attempt  has  been  made  to  copy  classic  details  in  dentil  courses, 
mutuals  and  frieze  moldings.  Certainly,  the  use  of  such  ornament  in  a 
building  of  this  character  would  have  been  frivolous  and  misplaced,  and 
particularly  unfortunate  because  of  the  probably  unsatisfactory  results 
which  would  have  been  unavoidable. 


Fig.  8. — A  beautiful  house  in  which  concrete  has  been  consistently  treated 

throughout. 

The  illustration  under  discussion  shows  conclusively  that  the  success 
of  a  concrete  building  architecturally,  depends  more  upon  the  proportion 
of  the  mass,  the  arrangement  of  the  voids,  or  window  and  door  openings, 
and  in  the  true  expression  of  the  material  used  than  upon  any  features 
which  may  be  denominated  as  architectural  ornamentation.  How  suc- 
cessful this  house  is  when  built  of  concrete  can  be  better  understood  by 

[28  1 


attempting  to  consider  it  when  constructed  of  any  other  material.  For 
instance,  the  imagination  could  not  see  any  beauty  in  a  building  of  this 
design  if  made  of  wood,  in  which  the  walls  were  of  weather-boarding  or 
shingles.  If  constructed  of  squared  ashlar,  it  would  certainly  have  the 
formidable  appearance  of  a  fortification,  and  as  a  dwelling  house  would 
be  still  more  undesirable  if  made  of  rubble  masonry.     It  is  certain  that 


BMnHHHHMIHHnMniHl 

Fig.  9. — A  small  house  of  simple  design  expressive  of  monolithic  construction. 


no  more  successful  use  of  concrete  could  have  been  made  for  a  house  of 
these  proportions  and  surroundings. 

That  concrete  is  as  adaptable  to  the  construction  of  smaller  houses, 
and  can  be  used  with  success  from  an  architectural  standpoint  for  a 
house  of  entirely  different  design  and  surroundings  from  that  which 
was  described  above,  is  shown  in  Fig.  9.  This  house  is  fortunate 
in  the  design  of  the  porch,  and  the  entire  structure  has  been  handled 

[29] 


with  a  simplicity  which  is  pleasing,  and  expressive  of  monolithic  con- 
struction. 

A  very  excellent  expression,  also,  of  the  best  that  has  been  done  in 
monolithic  construction  for  housework  is  shown  in  Fig.  io,  and  while  this 
conception  has  not  the  simplicity  of  the  two  residences  previously  de- 
scribed, it  shows  in  the  long  sweep  of  the  span  over  the  porch  entrance, 


Fig.  io. — A  second  example  of  the  adaptability  of  concrete  to  long  span  con- 
struction.    Note  porch. 


and  in  the  simplicity  of  the  steps  and  balustrades  of  the  porch,  an  ex- 
cellent use  of  the  material.  While  one  feels  that  there  is  a  restlessness  in 
the  spacing  and  proportions  of  the  window  openings,  and  in  the  topping 
out  of  the  porch  posts  with  the  somewhat  conventional  ornamentation, 
yet,  in  general,  this  dwelling  has  a  far  better  appearance  than  some  of  the 
accepted  best  work  of  houses  built  of  wood  and  stone. 

Another  example  of  concrete   house  construction  which  has  much 

[30] 


to  commend  it  is  illustrated  in  Fig.  II.  One  cannot  help  but  feel  that 
a  mistake  has  been  made  so  far  as  the  architectural  design  is  concerned 
in  using  the  evidently  wooden  beams  and  porch  rails  at  the  roof  of  the 
porch,  and  also  that  the  roof  and  dormer  are  hardly  consistent  in  wood 
with  the  monolithic  and  massive  lower  portion  of  the  house.  At  the 
same  time  the  simplicity  and  general  mass  and  proportion  of  voids  to  wall 


Fig.  II. — A  house  of  commendable  simplicity,  but  inconsistent  in  its  timber 

accessories. 


surface  is  most  excellent,  and  would  be  still  more  appreciated  if  the  photo- 
graph showed  the  deeper  shadows  which  would  occur  with  bright  sunlight. 
If  there  is  one  style  of  architecture  with  which  monolithic  concrete 
construction  fits  better  than  another,  it  is  the  California  or  Mexican 
"Mission,"  as  expressed  in  the  low  rambling  buildings  with  the  deep  re- 
cessed porches  and  Spanish  tiled  roofs  so  favorably  known  and  extensively 
used  in  California. 

[  3i  J 


A  costly  and  interesting  example  of  residence  construction  of  this 
type  is  shown  in  Fig.  12.  Everything  in  the  design  is  indicative  of  the 
strength  and  monolithic  possibilities  of  the  material.  One  will  notice 
upon  close  examination  that  the  face  of  the  porch  wall  near  the  base  of 
the  piers  sweeps  out  in  a  radius,  and  that  the  base  of  the  bay  window  on 
the  side  is  also  strengthened  and  made  interesting  by  a  sweeping  and 


Fig.  12. — Typical  California  or  "Mission"  house.    A  type  admirably  adapted 
to  concrete  construction. 


broadening  curve  toward  the  foundation.  The  formation  or  outline 
of  the  gable  walls  could  only  be  expressed  properly  in  a  material  like 
concrete,  which  could  be  molded  to  the  required  form.  One  feels  that 
the  color  scheme  is  expressive  of  harmony,  a  pleasing  combination  of 
flowers,  tropical  foliage,  and  red-tiled  roof,  all  emphasized  by  the  deep 
shadows  and  bright  sunshine  of  a  semi-tropical  land. 

[32] 


While  monolithic  concrete  for  house  construction  is  possible  of  great 
development  in  the  way  of  particular  and  pleasing  styles  cf  architecture, 
it  has,  in  the  hands  of  skilled  designers,  attained  beautiful  and  picturesque 
results  when  used  with  other  materials  in  following  the  older  types  of 
country  house  construction.  In  Fig.  13  is  shown  how  reinforced  con- 
crete may  be  successfully  used  in  the  construction  of  a  "Colonial"  country 


Fig.  13. — Attractive  use  of  concrete  as  adapted  to  familiar  types  of  the  country 

house. 

house.  The  entire  effect  of  this  residence  is  one  of  repose  and  dignity, 
and  its  proportions  and  details  are  such  as  to  class  it  with  the  suburban 
architecture  of  best  Colonial  type. 

The  use  of  concrete  in    the  construction  of  a  modern  suburban 

home  in  which  the  effort  has  been  only  to  follow  the  most  recent  style 

of  suburban   house  architecture  without  any  special  emphasis  of  the 

character  of  the  material,  is  shown  in  the  very  successful  design  illustrated 

3  [33] 


in  Fig.  14.  This  house  was  built  with  monolithic  walls,  and  is  extremely 
pleasing  in  the  accomplished  simplicity  and  interesting  details  of  the 
front  and  side  of  the  building  shown  in  the  perspective. 

Concrete  has  been  considerably  used  in  combination  with  other 
materials,  and  the  success  of  the  combination  can  be  seen  in  Fig.  15. 
Here  the  two  ends  of  the  structure,  which  is  a  twelve-roomed  country 
house,  are  made  interesting  by  the  rubble  work  indicating  the  chimney- 
breast  and  chimney,  and  the  use  of  boulders  to  bring  out  and  enhance 
the  appearance  of  the  plain  concrete  wall  must  be  commended.  The 
entire  design,  with  the  rubble  entrance  posts  supporting  the  open  timber 
trestle,  together  with  the  tile  roof  and  wide-extending  eaves,  makes  a 
picturesque  and,  on  the  whole,  pleasing  and  homelike  concrete  house 
composition. 

Architectural  Details  of  Monolithic  Concrete. — While  the  best  archi- 
tectural effects  have  been  obtained  in  those  houses  which  have  been  con- 
structed entirely  of  concrete,  by  a  careful  study  of  the  proportions  of 
the  building  and  the  arrangement  and  location  of  the  window  and  door 
openings,  and  arches  and  supports  of  porch  construction,  yet  it  is  fre- 
quently desired  both  by  the  owner  and  the  architect  that  concrete  dwell- 
ings should  have  some  ornamentation.  It  is  hardly  necessary,  nor  does 
it  lend  to  the  app'earance  of  the  building,  to  attempt  to  ornament  concrete 
houses  located  in  the  country,  or  in  truly  suburban  districts.  In  the 
construction,  however,  of  villas,  and  of  houses  located  in  the  more  pre- 
tentious parts  of  provincial  towns  and  cities,  there  is  probably  some  ex- 
cuse for  the  use  of  ornamentation  and  embellishment  of  concrete  ex- 
teriors. 

A  study  of  architectural  details  for  reinforced  concrete  house  con- 
struction will  certainly  show  that  the  finer  details  of  the  classic,  or  a  full 
revival  of  the  classic  or  Renaissance  architecture,  arc  not  suitable  when 
applied  to  the  decoration  of  dwellings  of  concrete.  For  instance,  such  a 
detail  as  that  shown  in  Fig.  16  is  of  a  degree  of  fineness  incompatible  with 
its  being  made  of  cement  or  concrete  and  used  in  conjunction  with  mono- 
lithic walls  for  house  decoration.     On  the  other  hand,  a  detail  like  that 

[34l 


Fig.  14. — A  handsome  house  showing  successful  use  of  concrete,  but  without 
emphasizing  its  character. 


Fig.  15. — Interesting  example  of  the  combined  use  of  concrete  and  rubble  work. 

[35] 


Fig.   16. — Concrete  should  be  translated  into  simple  and  original  forms  as 
opposed  to  the  elaborate  detail  shown  above. 


illustrated  in  Fig.  17  is  consistent  with  the  nature  of  the  material,  and  em- 
bellishes  by  its  simplicity  the  monolithic  construction  of  which  it  is  a  part. 
If  the  architectural  details  or  ornamentations  are  to  be  cast 
monolithic  with  the  walls,  they  should  be  simple  and  bold  in  their  out- 
line, and  of  such  a  contour  that  the  forms  can  be  made  at  a  minimum 
expense,  and  at  the  same  time  the  perfection  of  detail  insured  and  left 
undamaged  by  the  removal  of  the  forms.  The  purpose  of  ornamental 
moldings,  band  courses  and  decorative  features  is  to  furnish,  by  the  de- 


vvyz. 


Fig.  17. — Restrained  embellishment,  consistent  with  the  simplicity  of  concrete. 

marcation  of  the  lights  and  shades  of  their  several  surfaces,  a  relief  and 
interest  to  the  otherwise  bare  and  box-like  form  of  the  building  produced 
by  the  plain  walls.  It  is  not  necessary  that  moldings,  especially  in  con- 
crete houses,  should  be  curved  after  the  fashion  of  the  crown  and  other 
moldings  in  classic  architecture.  They  are  equally  effective  for  the 
purpose  if  made  with  simple  intersecting  planes,  as  illustrated  in  Fig.  18 
at  (a),  (b),  and  (c). 

[37] 


Upon  comparing  details  suitable  for  cut  stone,  and  those  adaptable 
to  concrete  construction,  it  is  interesting  to  note  in  Fig.  19  how  the 
natures  of  the  two  materials  are  expressed  in  the  profiles  and  forms  of  the 


a  be 

Fig.    18. — Profiles  suitable   for  concrete  detail. 

window-sills  herewith  shown.     In  the  figure  at  (a)  is  a  consistent  detail  for 
a  cut  stone  sill,  such  as  would  be  used  in  Colonial  work  when  made  of 


Fig.  19. — The  more  simple  of  the  two  would  be  effective  in  concrete. 

marble  or  limestone.     This  expresses  the  curved   lines  of  the  classic, 
while  the  detail  shown  at  (b),  though   probably  lacking  in   the  beauty 

[38] 


of  the  classic  curves,  expresses  boldly  and  efficiently  a  monolithic 
material,  and  is  so  formed  that  it  can  be  successfully  used  in  such 
construction. 

In  concrete  house  design  the  most  interesting  part  of  the  facade  is  the 
porch  and  main  entrance,  and  owing  to  the  nature  of  the  material  such 
details  as  those  illustrated  in  Figs.  20  and  21  arc  always  interesting  and 
good.     When  the  designer  confines  himself  to  these  simple  forms,  the 


Fig.  20. — Fagade  of  simple  design  more  appropriate  than  elaborate  ornamen- 
tation. 

general  effect  of  the  dwelling  amply  repays  in  simplicity  for  the  omission 
of  more  elaborate  ornamentation. 

To  say  that  concrete  construction  as  applied  to  dwellings  should 
be  developed  along  original  and  simple  lines  does  not  mean  that  elaborate 
or  highly  ornamented  work  is  impracticable.  On  the  contrary,  the  most 
complex  and  intricate  patterns  can  be  reproduced  by  the  use  of  glue 
molds  if  the  architect  finds  it  necessary  to  embellish  his  building  with  a 
multitude  of  detail,  including  even  undercut  work.  This  can  be  done 
at   far   less  cost   than  would  be   the  case  if  the  design  were  carved  in 

[39] 


stone,  and,  moreover,  once  the  molds  are  made,  a  casting  may  be  re- 
peated indefinitely. 

Architectural  Details  of  Molded  and  Cast  Concrete. — It  is  desirable 
in  some  instances  to  incorporate  in  the  design  of  concrete  houses  decora- 
tive features  in  the  nature  of  spot  ornamentation,  cartouches,  medallions, 


Fig.  21. — A  porch  and  entrance  representing  direct  and  simple  treatment  of 

concrete. 


and  entablature  decorations  over  doors  and  windows.  It  is  seldom 
practical  to  cast  as  a  part  of  monolithic  concrete,  decorative  features  in 
the  nature  of  modeled  work,  which  includes  figures,  foliage  and  work  in 
bas-relief. 

There  are  two  reasons  why  decorative  features  should  not  be  made 
monolithic  with  the  structure.     One  is,  that  if  these  ornamentations  are 

[40] 


repeated  it  is  necessary  to  have  a  considerable  number  of  forms  and 
molds,  which  increases  the  expense,  and  another  and  very  excellent 
reason  exists  in  the  fact  that  it  is  difficult  to  produce  such  work  in 
concrete  without  liability  of  having  it  spoiled  in  the  process  of  cast- 
ing or  during  the  construction  of  the  building.  It  is,  therefore,  best 
to  make  such  ornamentations  in  cement  or  artificial  stone  and  either 
set  them  in  recesses  left  in  the  walls  or  else  set  them  when  the  walls  are 
being  cast. 

If  such  a  detail  as  is  indicated  in  Fig.  22  is  required  as  a  decorative 
feature  of  a  concrete  dwell- 
ing, the  color  and  texture  of 
the  material  of  which  the 
cartouche  or  ornamentation 
is  made  should  be  carefully 
studied  with  reference  to  that 
of  the  wall.  The  best  work 
that  has  been  done  in  the 
way  of  molded  and  cast 
cement  or  artificial  stone 
ornamentation  is  that  in 
which  the  work  has,  after 
being  cast,  been  gone  over 
by  hand  and  properly  chased 
and  undercut.  It  is  only  in 
this  way  that  character  can 

be  given  to  the  material,  and,  when  this  is  done,  the  work  compares  very 
favorably  with  the  best  work  in  carved  stone. 

It  is  by  the  use  of  separately  molded  panels  and  decorative  features 
cast  of  cement  that  suitable  character  and  an  element  of  decoration  can 
be  given  to  concrete  dwellings.  The  use  of  such  ornamentation  lends  to 
the  dignity  of  the  structure  from  the  fact  that  it  harmonizes  in  color,  and 
when  properly  modeled  and  executed  gives  the  peculiar  interest  always 
in  evidence  where  carved  work  is  used. 

Some  suggestions  of  the  possibilities  in  the  way  of  decorative  orna- 

[41] 


Fig.   22. — A    decorative    detail    that   compares 
favorably  with  costly  carved  stone  work. 


ment  cast  of  cement  or  made  of  artificial  stone  may  be  observed  in  Figs. 
23  and  24,  and  a  skilled  designer  can  use  such  details,  when  cast  separately 
from  the  building,  with  an  assurance  that  they  will  be  perfect  upon  the 
completion  of  the  structure. 


Architectural  Decoration  in  Color. — One  of  the  first  means  of  decorat- 
ing concrete  structures  was  to  introduce  band  courses  and  spot  ornamen- 
tation made  up  of  colored  tile  set  or  embedded  in  the  concrete,  in  more 

or  less  pleasing  color  har- 
mony or  contrast.  For  this 
purpose  tiles  of  different 
manufacturers  were  used, 
but  from  experience  it  has 
been  found  that  tiles  of 
uniform  color  and  texture 
throughout  were  more  satis- 
factory than  those  which  had 
been  slip-glazed,  or  in  which 
the  color  was  only  in  the 
form  of  an  enamel.  While 
the  latter  is  approved  for 
interior  decoration,  such  as 
around  fireplaces,  it  has 
not  weathered  as  well  as  it 
should  when  used  on  the 
exterior  of  buildings.  It  has  crazed,  and  in  some  cases  the  entire  enameled 
surface  has  disappeared  from  the  tile. 

Therefore,  a  good  rule  to  observe  in  the  use  of  colored  tile  for  decora- 
tive schemes  in  concrete  houses  is  to  employ  only  tile  of  natural  color 
throughout.  Such  tile  should  be  selected  with  reference  to  its  color 
permanency. 

In  the  use  of  tile  mosaic  and  similar  surface  color  decoration  the 
best  effects  are  obtained  by  using  such  ornamentation  sparingly.  The 
design  should  be  carefully  studied  with  reference  to  color  and  the  ar- 

[42] 


Fig. 


-A  fine  example  of  separately  east  con- 
crete detail. 


rangement  of  the  tile,  and  must  be  placed  with  absolute  accuracy,  as 
otherwise  the  entire  effect  of  the  ornament  would  be  lost,  and  it  would 
become,  instead  of  an  in- 
teresting detail,  a  blemish. 
This  is  best  understood  by 
referring  to  Fig.  25,  which 
shows  a  carefully  studied 
doorway  with  mosaic  inlay 
on  the  two  main  piers. 
These  are  so  near  the  eye 
that  they  are  subjected  to 
close  scrutiny,  and  if  they 
were  not  placed  exactly  cen- 
tral, plumb  and  level,  the 
appearance  of  this  beautiful 
detail  would  be  spoiled.  This 
doorway  is  a  very  interesting 
example  of  what  can  be  done 
with  monolithic  concrete 
properly  proportioned  and 
studied. 

Instead  of  using  tiles 
and  mosaics  for  color  effect, 
very  elaborate  and  rich  orna- 
mentation of  polychrome 
terra-cotta  can  be  worked 
out  and  has  been  successfully 
used.  There  are  great  dec- 
orative possibilities  in  the 
proper  use  of  this  material, 
from  the  fact  that  any  shade 
and  color  can  be  produced 
upon  the  most  richly  molded 

surface.     Where  bold  ornamentation  is  required  for  cartouches,  brackets, 

I  43  J 


Fig.  24. — Pedestal  showing  the  adaptability  of 
concrete  to  elaborate  undercut  work. 


and  panels  in  colors,  nothing  is  as  admirably  adapted  to  the  beautifying 
of  concrete  surfaces  as  terra-cotta,  either  in  glazed  or  dull  colors. 

Color  effects  can  also  be  obtained  for  the  decoration  of  freize  courses 
and  flat  medallions  or  panels,  by  using  for  such  local  or  spot  ornamenta- 
tion, colored  aggregates,  which  may  be  cast  in  slabs  separately  and  set  in 
place,  or,  in  some  instances,  could,  by  the  arrangement  of  the  forms,  be 
cast  monolithic  with  the  walls.  This  form  of  ornamentation  will  hardly 
appeal  to  the  architectural  designer  except  for  interior  decoration,  for 
such  features  as  fireplaces,  panels  in  vestibules,  and  work  of  this  character. 

The  Decorative  Features  of  Timber  Construction  for  Concrete  Houses. 
— It  must  not  be  considered  that  reinforced  concrete  is  not  generally 
adaptable  to  other  than  the  peculiar  style  of  structure  to  which  it  seems 
to  lend  itself  so  admirably.  There  has  been  and  still  is  a  considerable 
demand  for  what  is  known  as  the  "English  half-timber"  country  house, 
and  reinforced  concrete  walls  worked  up  with  wood  half-timber  construc- 
tion securely  fastened  in  place,  or  embedded  in  the  concrete,  give  a  much 
more  permanent  and  substantial  construction  than  the  usual  half-timber 
work  consisting  of  batten  boards  with  metal  lathe  and  cement  plaster 
between  them.  In  the  hands  of  a  skilful  designer  reinforced  concrete 
can  be  used  very  successfully  with  half-timber  construction,  and  an  ex- 
cellent example  of  it  so  applied  is  shown  in  Fig.  26. 

Nor  is  the  use  of  wood  in  connection  with  concrete  walls  confined  to 
the  "half-timber"  construction,  but  may  readily  be  used  as  illustrated 
in  Fig.  27,  which  shows  the  entrance  to  a  residence  built  of  concrete  with 
monolithic  walls.  Further  possibilities  of  wood  and  timber  construction 
in  connection  with  the  monolithic  concrete  are  shown  in  the  picture  of 
the  front  porch  of  the  same  house.  The  neatly  profiled  projecting  ends 
of  the  porch  timber,  resting  upon  the  beautifully  molded  pillars,  can  but 
give  interest  and  attraction  to  this  well-designed  suburban  residence. 
Even  the  porch  rail,  though  of  wood,  is  of  such  simplicity  as  to  harmonize 
well  with  the  clean  outline  and  dignified  plainness  of  the  porch  walls  and 
outside  construction. 

Interior    Decoration    and    Details. — Reinforced     concrete    interior 

[44] 


Hg.  2". — Porch  showing  combination  of  timber  and  monolithic  construction. 

[47) 


details  must  necessarily  be  plain  and  simple  in  their  profiles,  though  if 
artificial  stone  or  cast  cement  is  used,  decorative  features  for  fireplaces 
can  be  replete  with  ornamentation.  To  illustrate  some  of  the  best  in- 
terior details  in  concrete,  the  attention  is  called  to  the  fireplace  shown  in 
Fig.  28.  This  fireplace  is  refined  in  the  extreme,  and  is  a  relief  when  com- 
pared with  the  stock  mill- 
constructed  affairs  so  often 
seen  in  the  modern  house. 

Even  more  plain,  but 
quite  effective,  is  the  fire- 
place shown  in  Fig.  29.  This 
substantial  design  conveys 
the  sense  of  security  and 
durability  always  desirable 
in  a  fireplace.  The  rough 
lintel  is  in  pleasing  contrast 
with  the  smoother  surface, 
and  the  work  throughout  is 
simple  and  direct,  showing 
how  effective  concrete  work 
can  be  made. 

Somewhat  more  elabor- 
ate, but  still  interesting,  are 
the  fireplaces  shown  in  Figs. 
30  and  3 1 .  That  in  the  former 
illustrates  how  monotony  in 
design  may  be  relieved  by  the 
introduction  of  figures  or  de- 
signs in  low  or  high  relief. 
Where  beam  and  slab  construction  is  used  for  the  floors  in  houses  of 
larger  size,  the  concrete  beams  and  girders  make  admirable  beamed  ceil- 
ing effects.  Usually  it  is  customary  to  plaster  the  concrete  with  a  white 
coat,  but  a  good  decorator  could  finish  the  rough  concrete  so  as  to  give 
rich  effects  by  means  of  carefully  studied  color  schemes  and  stencilled 

[  48] 


^L       1 

1 

.           1?^ 

Fig.  28. — Concrete  fireplace  with  plain  and  sim- 
ple profile. 


Fig.   29. — Effective  concrete  work  expressed  in  dignified  design. 


Fig.  30. — Example  of  smooth  and  rough  textures  in  surface  finish. 

[49] 


Fig.   31. — Elaborate   but   interesting   treatment   of  concrete. 


Ii;<.    32.     Example   of   beautiful   and   dignified   interior  construction. 

I  5o] 


ornament.  To  illustrate  how  beautiful  and  dignified  an  interior  of  this 
construction  can  be  the  attention  is  called  to  Fig.  32.  It  only  requires, 
in  constructions  of  this  kind,  for  the  best  effect  obtainable,  to  have  the 
beams  go  central  over  points  of  support,  and  to  study  the  panelling  of  the 
beams  and  girders  of  the  ceiling  so  as  to  obtain  symmetry  and  equality 
of  spacing. 

There  are  possibilities  in  concrete  for  the  most  interesting  stair  con- 
structions. Concrete  is  adaptable  to  such  a  variety  of  forms,  and  when 
properly  reinforced,  so  self-supporting,  that  the  lines  of  the  usual  con- 
ventional stairs  or  steps  can  be  departed  from  radically.  Spiral  or  flying 
stairways,  with  graceful,  sweeping  horses  and  rails,  are  entirely  practical 
and  possible  at  a  minimum  cost  in  concrete  construction. 

The  possibilities  of  this  material  for  both  the  construction  of  the 
stair  and  the  rail  are  shown  in  Fig.  33,  and  whether  the  entire  stairway 
and  rail  are  of  monolithic  construction,  as  illustrated  in  this  photograph, 
or  whether  other  materials  are  used  for  embellishment,  it  is  certain  that 
for  interest,  simplicity,  and  beauty  there  are  few  rivals  to  that  shown  in 
the  figure. 


[52 


Chapter  III 
Details  of  Construction 


A  doorway  showing  the  adaptability  of  concrete  to  either  plain  or  ornamental 
work.  Note  the  great  contrast  between  the  elaborate  undercut  floral 
decoration  and  the  simple  units  comprising  the  structural  features. 


54 


Chapter  III 
Details  of  Construction 

Types  of  Floor  Construction. — In  building  construction  there  are  practi- 
cally four  types  of  floor  construction,  when  classified  as  to  their  structural 
formation.  These  are  the  flat  slab,  the  beam  and  girder,  the  hollow  tile 
and  concrete  joist  construction,  and  what  is  known  as  panel  construction. 

The  simplest  form  is  the  flat  slab  of  concrete,  supported  by  walls  or 
partitions,  and  of  sufficient  thickness  and  reinforcement  to  span  the 
intervening  space  between  the  walls. 


Fig.  34.— Slab  and  beam  construction. 


Where  the  spans  are  too  great  for  a  flat  slab,  it  is  then  usual  to  sup- 
port the  concrete  slab  on  concrete  beams  and  girders  which  are  monolithic 
with  the  slab,  and  which  have  the  general  appearance  indicated  in  Fig.  34. 

In  buildings  where  the  floor  loads  are  comparatively  light,  a  type 
of  construction  known  as  the  concrete  joist  construction  has  been  exten- 
sively used.  A  section  through  such  a  floor  is  illustrated  in  Fig.  35  at 
(a)  and  (b).  In  each  of  these  sections  it  will  be  noticed  that  both  of 
the  main  supports  of  the  floor  are  concrete  joists,  reinforced  with  steel 
rods,  and  the  intervening  space  between  the  joists  is  filled  in  with  hollow 

I  55  I 


terra-cotta  tile.  The  illustration  at  (a)  shows  this  type  of  construction 
for  floors  where  the  load  is  very  light,  and  where  the  rectangular  joists 
are  strong  enough  to  carry  their  portion  of  the  load  from  center  to  center 
of  the  adjacent  tile.  In  Fig.  35  (b)  is  illustrated  a  construction  which 
is  stronger  than  that  shown  at  (a),  from  the  fact  that  several  inches  of 
concrete  are  placed  upon  the  top  of  the  tile,  and  being  monolithic  with  the 
concrete  joists,  additional  compressive  area  is  provided,  thus  insuring  the 
capability  of  the  floor  for  carrying  greater  loads.     The  purpose  of  the 


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Fig.  35. — Floor  sections,  showing  arrangement  of  concrete  and  hollow  tile  of 

concrete. 


hollow  tile  in  this  floor  construction  is  purely  to  fill  in  the  space  between 
the  joists,  and  to  form  sides  into  which  the  concrete  can  be  poured.  The 
tile  also  provides  a  plastering  surface  to  form  a  flat  ceiling. 

The  advocates  of  the  hollow  tile  and  concrete  joist  floor  constructions 
claim  that  the  adherence  of  the  concrete  to  the  sides  of  the  hollow  tile 
insures  greater  strength  in  the  floor  construction  because  the  upper  one 
or  two  inches  of  the  tile  adds  to  the  compressive  resistance  of  the  concrete, 

I  56] 


or,  at  least,  extends  the  area  of  compression  in  the  upper  part  of  the 
system. 

There  are  several  varieties  of  the  hollow  tile  and  concrete  joist  con- 
struction, and  one  of  the  most  recent  of  these  types,  known  as  the  "  Hin- 
ton"  system,  is  illustrated  in  Fig.  36.  Upon  examination  of  this  illus- 
tration it  will  be  seen  that  instead  of  forming  the  hollow  tile  blocks  with 
vertical  sides,  the  sides  are  splayed  in  such  a  manner  as  to  make  the  con- 
crete joists  wide  at  the  top  and  narrow  where  reinforced  with  the  steel. 
By  the  use  of  such  a  block  the  compressive  area  of  the  concrete  is  increased, 
and  less  concrete  is  used,  as  it  is  saved  where  not  required,  namely,  below 
the  neutral  axis.  A  third  merit  claimed  is  that  the  tiles  almost  meet  at 
the  bottom  and  form  a  uniform  material  for  plastering.     This  is  of  some 


Fig.  36. — Arrangement  of  concrete  and  hollow  splayed  tile. 


advantage  where  the  ceiling  is  to  be  painted  or  decorated,  as  the  possi- 
bility of  different  markings  or  discolorations  by  the  two  materials  is 
avoided. 

The  panel  construction  differs  little  from  the  flat  slab  construction, 
except  the  slab  is  supported  upon  beams  on  all  four  sides  without  inter- 
mediate beams,  and  the  slab  is  usually  reinforced  in  two  directions.  Some- 
times the  flat  slab  is  simply  supported  upon  posts  or  columns  of  concrete 
which  are  spread  at  the  top.  This  relieves  the  slab  for  some  distance 
out  from  the  column,  thus  reducing  the  stresses.  To  such  systems  the 
name  of  "mushroom"  has  been  given,  though  there  are  three  or  more 
similar  systems  variously  known.     These  systems  have  not  as  yet  been 

[  57  1 


(a) 


much  used  in  house  construction,  though  they  could  well  be  employed  in 
more  pretentious  work. 

Methods  and  Types  of  Steel  Reinforcement— In  reinforcing  con- 
crete, plain  round  bars  have  been  used  successfully,  and  buildings  which 
have  been  so  reinforced  have  withstood  all  stresses  and  vibrations.  There 
is,  however,  a  general  preference  for  some  type  of  bar  or  reinforcing  rod 
which  gives  a  greater  bond  in  the  concrete;    that  is,  the  bar  is  rolled,  or 

formed  with  projections,  so 
that  when  embedded  in  the 
concrete  it  would  require  a 
greater  force  to  withdraw  it 
than  a  plain  bar.  Bars  which 
have  been  specially  rolled  or 
formed  for  reinforcing  concrete 
W  are    known    as     "deformed" 

bars.  There  are  so  many 
types  of  these  bars  that  it  is 
impossible  to  illustrate  them 
all,  and  consequently  only  a 
few  of  the  older  and  more 
usual  forms  are  given.  These 
bars  are  shown  in  Fig.  37,  at 
(a),  (b),  (c),  and  (d). 

The  figure  at   (a)  repre- 
sents a  "square  twisted  "  steel 
bar.     This  type  of  bar  is  ex- 
tensively used,  as  there  is  no  patent  on  it,  and  the  additional  cost  of  the 
twisting  is  slight.     It  is  probably  more  used  than  all  of  the  rest  of  the 
reinforcing  bars  on  the  market. 

In  the  figure  at  (b)  there  is  illustrated  what  is  known  as  the  "cor- 
rugated" bar.  This  is  one  of  the  first  deformed  bars  put  on  the  market, 
and  gives  a  maximum  cross  section,  and  a  good  deformation  with  a 
minimum  increase  in  weight. 

l5«l 


^^Wj^/A 


'(<■) 


I'  |R-  37- — Types  of  reinforcement. 


The  bar  at  (c)  is  known  as  the  Kahn  bar,  in  which  the  deformation  is 
practically  obtained  by  shearing  the  stirrups  and  bending  them  directly 
from  the  rolled  fins  on  the  sides  of  the  bar.  This  bar  is  made  in  many 
sizes  and  several  different  sections. 

While  there  have  been  many  different  types  of  deformed  bars  placed 
on  the  market,  those  shown  may  be  considered  as  representative,  and  are 
quite  commonly  used. 

In  the  reinforcement  of  slabs  in  house  construction  expanded  metal 
or  woven  wire  may  be  conveniently  and  cheaply  employed.  The  latter 
is  particularly  good  from  the  fact  that  it  is  woven  with  large  wires  in  one 


Fig-  38. — Example  of  fabricated  reinforcement. 


direction  and  small  wires  in  the  other,  making  it  economical  for  slabs  of 
rectangular  shape  reinforced  in  two  directions.  This  reinforcement  is 
shown  at  (d)  in  the  figure. 

As  reinforced  concrete  construction  was  developed  there  were  a 
number  of  types  of  steel  reinforcement  placed  on  the  market  in  the  nature 
of  fabricated  material,  in  which  the  several  reinforcing  rods  and  bars, 
together  with  the  stirrups,  were  held  together  in  a  frame  or  unit.  In 
general  practice,  however,  there  seems  to  be  a  preference  among  con- 
tractors to  use  what  is  known  as  the  "loose  bar"  system,  illustrated  in 
Fig.  38.  Here  the  several  straight  bars  and  trussed  bars  are  cut  to  length, 
bent  cither  in  the  shop  or  at  the  building,  and  are  placed  in  the  form 

(59  1 


separately.  Sometimes  they  are  supported  from  the  bottom  of  the  forms 
by  means  of  small  cast  blocks  of  cement,  or  else  are  tied  together  with 
sheet  iron  or  bar  iron  supporters,  and  are  held  in  place  by  wiring,  or  sup- 
ported on  the  stirrups  which  rest  upon  the  top  of  the  centering.  The 
stirrups  are  sometimes  wired  to  the  steel  reinforcing  bars,  and  are  held 
at  the  proper  distance  apart  by  a  rod,  to  which  they  are  secured  by 
wire. 

While  the  loose  bar  system  causes  additional  work  in  the  field, 
it  is  a  question  whether  any  of  the  patented  systems  of  fabricated  frames 
can  compete  in  cost,  from  the  fact  that  there  is  royalty  to  pay,  additional 
care  in  handling,  and  sometimes  additional  freight  rates,  due  to  a  differ- 
ent freight  classification. 


Fig.  39- 


One  of  the  best  fabricated  systems  of  steel  reinforcement  is  that 
illustrated  in  Fig.  39.  This  system  is  very  practical,  and  from  the  fact 
that  it  can  be  shipped  in  a  flat  condition  and  pulled  into  shape,  is  very 
conveniently  handled,  and  can  probably  be  purchased  in  the  shop  for  less 
cost  than  most  of  the  fabricated  systems  on  the  market. 

Another  system  of  girder  frame  that  can  be  used  particularly  in 
house  construction  is  what  is  known  as  the  electric  welded  frame,  il- 
lustrated in  Fig.  40.  In  this  frame  the  stirrups  are  welded  to  the  rein- 
forcing bars.  By  this  arrangement  the  proper  amount  of  the  steel  re- 
inforcement for  any  beam  or  girder  is  insured,  and  the  number  and  spac- 
ing of  the  stirrups  fixed.  It  is  also  in  a  very  convenient  form  for  ship- 
ment. 

[60] 


Methods  of  Finishing  Floors. — Reinforced  concrete  floor  slabs  may 
be  finished  upon  the  top  with  any  material,  and  in  house  construction 
it  is  probable  that  wood  floors  are  the  most  desirable.  Some  houses 
have  been  built  with  concrete  floors,  especially  apartment  houses.  The 
concrete  finish  can  be  placed  directly  upon  the  reinforced  concrete  slab 


5firrup  We/ckdJo  3sr 


~ Section  of  Bar  Showing 
Sf/rrup 


Fig.  40. — Electrically  welded  frame  reinforcement. 

at  the  time  it  is  put  in  place,  or,  if  this  is  not  practical,  the  slab  can  be 
swept  clean,  washed  with  dilute  muriatic  acid,  the  acid  thoroughly  re- 
moved by  washing  with  water,  and  the  top  coat  worked  on.  This  method 
is  successful  when  care  is  used  in  the  application  and  workmanship  of 
the  top  finish.  A  section  of  a  floor  so  constructed  is  illustrated  in  Fig. 
41.     Usually  the  finish  is  1  inch  in  thickness,  and  sometimes  in  house 


Fig.  41. — Concrete  floor  slab  with  top 
coat. 


Fig.  42. — A  wooden  floor  on  concrete 
slab. 


work  brass  sockets  are  inserted  at  or  near  the  corners  of  rooms  so  that  the 
rugs  may  be  secured  in  place. 

Another  method  of  applying  a  concrete  finish  is  to  place  on  top  of 
the  concrete  slab,  some  time  after  it  has  been  poured,  two  inches  of  cinder 
concrete,  and  finish  with  the  one-inch  top  coat  as  described  above.  It 
is  usual  to  use  a  cinder  concrete  mixture  consisting  of  one  part  of  Portland 

f6i  1 


cement,  two  parts  of  sand  or  gravel,  and  six  parts  of  clean  boiler  cinders. 
In  the  top  coat  use  one  part  Portland  cement,  one  part  sand,  and  one 
part  crushed  stone  or  granite  grits. 

When  a  wood  floor  is  desired,  and  this  would  ordinarily  be  used  in 
house  construction,  it  is  best  to  use  the  construction  illustrated  in  Fig.  42. 
Here  2"  x  3"  sleepers  are  laid,  16  inches  center  to  center,  upon  the  con- 
crete. Sometimes  nails  are  driven  in  the  side  of  the  sleeper  and  the 
space  between  is  filled  with  cinder  concrete,  this  being  made  level  with  the 
top  of  the  sleepers.  Either  a  rough  floor  to  receive  a  fine  hardwood 
floor,  or  the  finished  floor,  is  laid  directly  upon  the  sleepers.  It  would  be 
best  in  house  construction,  if  the  finished  floor  is  to  be  laid  directly  upon 
the  sleepers,  to  paint  the  back  of  the  flooring,  so  that  any  moisture  that 
may  remain  in  the  sleepers  or  in  the  cinder  concrete  will  not  warp  and 
twist  the  flooring. 

Roof  Construction. — The  roofs  of  concrete  houses  should  necessarily 
be  entirely  fireproof,  and  consequently  the  roof  covering  should  be  sup- 
ported upon  a  construction  which  will  not  ignite  and  burn.  A  house, 
however,  differs  from  the  manufacturing  building  or  warehouse  with  re- 
gard to  the  roof  construction  in  that  it  is  not  likely  to  be  subject  to  the 
shock  and  weight  from  falling  walls,  or  the  debris  from  adjacent  structures 
on  fire.  It  can  therefore  be  of  lighter  construction  than  is  usually  re- 
quired for  fireproof  commercial  buildings  of  reinforced  concrete.  It  must 
also  be  considered  that  the  roof  of  a  house,  in  its  slopes,  intersections,  and 
skylines,  has  much  to  do  with  the  architectural  appearance  of  the  build- 
ing. The  construction  is,  therefore,  considerably  influenced  by  the  gen- 
eral formation  of  the  roof,  that  is  to  say,  whether  it  is  flat  or  sloped. 
The  degree  of  slope  also  influences  the  roof  covering. 

In  buildings  which  arc  designed  on  classic  lines,  having  square  para- 
pets and  flat  roofs,  there  is  probably  no  better  construction  than  a  rein- 
forced roof  slab.  This  slab  is  carried  upon  beams  and  girders  in  the  same 
manner  as  the  floor  construction,  and  may  be  built  either  with  a  slope  or 
flat.  To  drain  the  flat  roof,  build  up  the  cinder  concrete  as  indicated  in 
Fig.  43.     The  advantage  of  constructing  the  roof  in  this  manner  is  that 

I62I 


A  frank  and  direct  use  of  concrete  designed  with  reference  to  economy,  utility,  and 

minimum  cost  for  up-keep. 


[64] 


quite  frequently  the  forms  used  for  the  floor  construction  can  be  used  for 
the  roof  forms.  The  additional  thickness  of  the  cinder  concrete  gives 
insulation  against  temperature  changes. 

The  proper  covering  for  a  flat  concrete  house  roof,  which  does  not 
appear  in  the  perspective  or  elevations  of  the  building,  is  either  some 
form  of  prepared  roofing  or  else  4-ply  slag  and  gravel  roof.  Many 
of  these  roofs  are  guaranteed  for  a  period  of  ten  years,  and  are  entirely 
serviceable  and  satisfactory. 

In  placing  such  a  roof  it  is  the  usual  practice  to  smooth  over  the  top 
of  the  cinder  concrete  forming  the  slope  of  the  roof  with  cement  mortar, 
so  as  not  to  have  any  projecting  stones  or  edges  of  aggregates,  which  are 
likely  to  cut  through  felt.     Then  the  first  layer  of  felt  is  well  secured  to 


Fig.  43. — Flat  slab  roof  with  cinder  concrete  top  coat  sloped  for  drainage. 

the  concrete  with  hot  pitch.  This  has  always  been  sufficient  to  hold  the 
roofing  in  place.  It  is  good  practice  to  build  up  gussets  around  all  the 
parapet  walls,  and  run  the  felt  up  and  under  some  form  of  coping  tile, 
or  else  in  cheaper  work,  fasten  it  under  a  cleat  which  is  secured  to  nailing 
strips  left  in  the  concrete.  These  two  forms  of  construction  are  shown 
at  (a)  and  (b)  in  Fig.  44. 

The  extent  of  flat  roofs  in  house  construction  is  such  that  it  is  entirely 
safe  to  make  a  concrete  roof  slab  and  cover  it  with  a  top  coat  of  a  damp- 
proof  cement  mixture,  thus  doing  without  any  roofing  material.  Shrinkage 
or  settlement  cracks  may  occur,  however,  and  the  integrity  of  the  roof  is, 
of  course,  destroyed  if  it  does  crack. 

This  danger  of  concrete  cracking  is  reduced  to  a  minimum  where  the 
5  [65] 


areas  of  the  roof  are  small,  such  as  would  be  the  case  in  house  construc- 
tion, and  could  be  entirely  obviated  by  dividing  the  roof  up  in  sections 
and  putting  in  expansion  joints,  as  illustrated  in  Fig.  45.  In  this  con- 
struction a  V-shaped  piece  of  copper  is  placed  on  the  forms  or  centering, 
and  embedded  in  the  concrete  slab,  the  joint  being  afterward  raked  out 
and  filled  with  asphalt  or  mastic  cement.  In  using  asphaltic  prepara- 
tions for  filling  a  joint  of  this  kind  the  best  result  is  obtained  by  heating 
the  crevice  with  a  torch  before  the  asphalt  is  poured  in. 


Telf  Flashing 
^■Wood  deaf 

inder  Concrete 


(a)  (b) 

Fig.  44. — Two  types  of  concrete  roof  construction  combined  with  felt  covering. 


Where  the  roof  of  a  concrete  house  is  flat,  and  where  the  item  of 
cost  is  not  a  consideration,  one  of  the  best  roof  coverings  is  flat  or  prom- 
enade tile,  laid  in  bitumastic  cement.  Such  roofs  are  very  desirable 
where  it  is  proposed  to  use  the  roof  as  a  roof-garden  or  observatory.  A 
somewhat  cheaper  way  of  accomplishing  the  same  result  is  to  cover  the 
concrete  roof  slab,  after  it  has  been  smoothed  off  with  cement,  with  a 
prepared  or  felt  roof  covering,  and  then  placing  on  this  covering  a  thick 
concrete  finish  for  a  wearing  surface — at  least  1  ^2  inches  thick — marked 
off  in  blocks  for  appearance. 

[66  1 


Copper   5+n'p 
Fig.  45 


Method  of  constructing  expansion 
joints  and  applying  filler. 


As  the  roofs  of  houses  are  subjected  to  extremely  light  loads,  they  can 
be  economically  constructed  with  rectangular  concrete  beams,  either  cast 
in  place  or  cast  on  the  ground  and  used  as  joists,  and  then  covered  with 
some  material  such  as  trussed  metal  lath,  or  ferro-inclave,  the  former 
being  illustrated  at  (a),  Fig.  46,  and  the  latter  at  (b).  The  advantage  of  using 
these  is  due  to  the  fact  that  no 

centering  is  required.     They  are  *-  Asphalt  or  tl*3t,e  Cement- 

arranged  to  plaster  with  cement 
mortar  on  both  sides,  and  a  re- 
inforced slab  is  thus  obtained 
sufficiently  strong  for  any  roof 
construction.  Such  construc- 
tion can  sometimes  be  used  at 
less  cost  than  a  monolithic  slab. 

In  the  use  of  such  materials,  wires  or  other  means  of  fastening 
phould  be  left  in  the  joist,  so  that  the  metal  reinforcing  sheets  can  be 
secured  to  them.  If  the  building  is  built  with  concrete  walls,  light  steel 
beams  can  be  used  for  framing  the  roof,  and  the  slab  construction  secured 

to  them,  though  the  use  of  such  steel 
beams  is  attended  by  a  diminution 
of  the  fireproof  properties,  provided 
they  are  not  in  turn  protected  by  a 
covering  of  at  least  a  ij^-inch  thick- 
ness of  concrete. 

If  it  is  desired  that  the  roof  of 
a  concrete  house  should  be  covered 
with  slate,  or  with  flat,  corrugated, 
or  special  interlocking  tile  or  asbestos 
shingles,  and  if  the  roof  is  sloping  and 
of  concrete  construction,  it  is  necessary  to  provide  some  means  by  which 
the  slate  or  tile  may  be  secured  to  it.  Quite  frequently  the  roof  is  con- 
structed with  cinder  concrete,  which  is  sufficiently  porous  to  allow  the 
nailing  of  furring  strips  to  the  top  of  the  roof,  so  that  the  slate  or  tile 
may  be  fastened  to  them.     The  best  practice  would  be  to  imbed  in  the 

[67] 


(a) 


(b) 


Fig.  46. — Metal  lath  and  ferro-inclave  re 
inforcement  in  light  roof  construction. 


concrete  nailing  strips,  and  cross-furr  the  roof  as  indicated  in  Fig.  47,  thus 
providing  a  secure  nailing  for  the  slate  or  tile.  The  spacing  of  the  furring 
strips  is  regulated  by  the  character  of  the  roof  covering.  The  strips  to 
which  the  furring  strips  are  fastened  should  be  nailed  to  them  with  solid 
copper  or  copper-sheathed  nails. 

The  construction  of  roofs  for  concrete  buildings,  as  to  gutters  and 
eaves,  varies  little  from  buildings  constructed  of  other  materials.  Con- 
crete, however,  has  an  advantage  in  that  overhanging  cornices  and  stop 
gutters  are  readily  constructed  and  molded,  and  may  be  flashed  in  any 

manner  by  using  furring  strips 


Nailing  Strips  -. 
Furring  Strip. 


S^\ 


Metal  lath 
Suspended  Ceding '  |* 


Fi^   47- — Details  of  roof  construction  where  slate 
or  tile  is  to  be  used. 


and  nailing  blocks  embedded 
in  the  concrete. 

Concrete  is  a  material  of 
such  great  durability  and  per- 
manency that  in  designing  the 
eaves  or  cornices  of  building% 
an  effort  should  be  made  to 
avoid  the  use  of  hanging  gut- 
ters of  metal.  The  best  results 
are  obtained  by  casting  stop 
gutters  or  recessed  gutters 
directly  in  the  concrete,  and 
making  these  damp-proof  by 
means  of  carefully  graded  aggregates,  thus  obtaining  a  dense  concrete,  or 
by  painting  with  waterproof  cement  paints,  or  by  lining  them  with  metal. 
Tin  is  not  a  good  material  for  the  formation  of  eave  boxes  and  the 
lining  of  gutters  of  concrete,  from  the  fact  that  placed  next  to  concrete  it 
docs  not  seem  to  be  as  durable  as  when  used  in  conjunction  with  wood 
construction.  Copper  or  lead  should  always  be  used  where  the  use  of 
metal  flashings  or  gutter  linings  is  unavoidable  or  desirable. 

Some  suggestions  for  the  construction  of  the  gutters  and  eaves  of 
concrete  dwellings  may  be  seen  in  Figs.  48,  49,  and  50.  In  the  first  men- 
tioned figure  there  is  shown  the  detail  at  the  eaves  of  a  building  con- 
structed with  concrete  walls  and  roof  slab,  and  having  for  the  roof  cover- 

[68  1 


ing  one  of  the  many  excellent  forms  of  interlocking  tile  roofs.  Here  the 
gutter  is  cast  directly  in  the  concrete  of  the  cornice,  and  is  flashed  with 
copper.  It  is  interesting  to  note  the  manner  in  which  the  copper  flashing 
is  secured  in  this  detail. 

Wide  projecting  eaves  are  admirably  adapted  to  the  design  of  con- 
crete houses.  The  detail  shown  in  Fig.  49  is  suggestive  of  the  manner  in 
which  the  gutters  for  such  roofs  could  be  arranged  so  as  to  secure  per- 


/n/rr/ocA/ng  TC  T/'/e 


changer 


Watert?roo/ec/  tvU/i  Vfe/erp/oof  Pa/nl 


j--P/c+ure  Mould/ho 


W/ft£/<?w  fra/ne 


Fig.  48. 


Fig.  49. 


Figs.  48  and  49. — Suggestions  for  the  construction  of  gutters  and  eaves  for  concrete 

dwellings. 


manency,  and  thus  avoid  the  trouble  so  likely  to  arise  with  galvanized 
iron  or  copper  hanging  gutters.  As  the'gutter  in  this  detail  is  well  out- 
side of  the  building  wall,  no  very  great  care  need  be  used  to  have  it  es- 
pecially water-tight,  so  that  the  metal  flashing  may  be  omitted,  and  the 
gutter  may  be  finished  with  a  cement  mortar  coating  made  waterproof 
by  the  use  of  properly  graded  aggregates;  or,  since  it  is  not  within  the 
range  of  vision,  it  could  be  coated  with  a  waterproof  paint. 

A  gutter  inexpensive  to  construct  is  shown  in  Fig.  50,  and  this  gutter 

[69] 


may  be  formed  in  a  variety  of  ways.     It  also  acts  as  a  good  snow-guard, 
is  efficient,  and  excellent  in  appearance. 

All  of  these  concrete  gutters  and  cornices  are  enduring,  and  have  the 
advantage  of  requiring  no  repair  expense,  an  item  very  frequent  with  the 
same  features  of  frame  houses  and  those  of  masonry  or  brick  having  the 
usual  wooden  roofs. 


Window  and  Door  Frame  Construction. — Since  concrete  is  a  mono- 
lithic material,  there  is  no  real  necessity  for  arching  window  or  door  open- 


Nj///t?a  3/<?e£?> 


Fig.  50. — Another  suggestion  for  the  construction  of  gutters  and  eaves  for  concrete 

dwellings. 

ings,  and  it  is  surely  very  inconsistent  to  accentuate  the  hoods  of  such 
openings  by  showing  arch  rings  marked  in  joinings  to  simulate  voussoirs. 
In  consequence,  the  window  and  door  openings  are  made  either  with  a 
square  head,  or,  if  the  architectural  design  requires,  are  formed  on  the 
curves,  either  segmental  or  three-centered,  though  such  arches  have  little 
structural  significance,  especially  where  the  concrete  is  reinforced  with 
steel  rods  or  bars. 

In  masonry  and  in  brick  structures  it  has  been  the  usual  practice  to 


Entrance  of  Albert  Kahn's  residence,  Detroit,  Mich.  Doorway  and  steps 
cast  in  solid  concrete.  A  striking  example  of  the  economy  of  concrete  as 
compared  with  cut  stone. 


(71 


build  up  window  or  door  frames  as  the  masonry  or  brickwork  progressed. 
While  this  can  be  done  with  concrete  construction,  it  is  not  the  best  prac- 
tice. In  pouring  the  wet  concrete  and  in  working  the  formwork  around 
the  openings  the  millwork  is  not  benefited,  as  any  excess  of  water  in  the 
concrete  is  apt  to  buckle  and  warp  the  millwork.  The  best  practice  is 
to  place  the  door  and  window  frames  after  the  wall,  with  its  openings, 
has  been  cast. 

In  the  setting  of  all  door  and  window  frames  the  primary  requisite 
is  to  obtain  a  weatherproof  joint  between  the  frame  and  wall  construction, 
both  at  the  jambs,  sill  and  head.  The  best  practice  in  window  construc- 
tion where  a  reveal  frame  is  used  is  to  rebate  the  wall  as  indicated  in  Fig. 
51,  and  in  constructing  the  window 
frame  to  make  it  of  such  a  size  that 
it  can  readily  be  placed  from  the  back. 
The  inside  face  of  the  frame  is  ex- 
tended to  scribe  to  the  opening,  as 
indicated  at  a,  and  by  this  means 
the  frame  can  be  secured  in  place  to 
wooden  nailing  blocks  set  in  the  con- 
crete, or  else  by  plugging  the  wall 
after  the  concrete  has  set. 

A  finish  is  secured  on  the  outside 
by  the  reveal  molding,  as  at  b,  and 

the  construction  made  further  weatherproof  by  the  casing,  as  shown  at  c. 
The  head  of  such  a  frame  can  be  designed  as  shown  in  Fig.  52,  both  the 
reveal  molding  and  the  inside  trim  being  around  the  head  of  the  frame, 
and  a  rebate  being  formed  in  the  concrete  at  the  head,  as  was  done  on  the 
jambs. 

While  concrete  sills  can  be  molded  monolithic  with  the  walls,  it  is 
far  better  to  mold  the  sills  separately  and  set  them  in  place,  constructing 
the  sill  of  the  window  frame  as  shown  in  detail  in  Fig.  53.  In  this  figure 
the  molded  treatment  or  artificial  stone  sill  is  shown  at  a,  the  wood  sill  of 
the  frame  at  b,  while  the  inside  trim  and  apron  are  indicated  at  c. 

In  the  best  work  an  effort  is  always  made  to  insure  a  weatherproof 

[73] 


Fig.  51. — Detail    of  weatherproof   joint 
between  frame  and  wall  construction. 


joint  between  the  wood  sill  and  the 
cement  sill,  and  the  best  practice  is 
to  insert  a  weatherstop,  as  shown  at 
d.  This  weatherstop  consists  of  a 
Y%'  x  i"  galvanized  strip,  which 
breaks  the  joint  between  the  wood 
and  cement  sills  by  entering  grooves 
formed  in  each,  thus  preventing  the 
entrance  of  moisture. 

What  was  said  with  reference  to 
the  jamb  and  hood  construction  for 
window  frames  applies  equally  to 
door  frames,  though  it  is  sometimes 
best  to  construct  door  frames  with- 
out a  rebated  jamb,  and  depend 
upon  some  other  means  to  make  a 
weatherproof  joint  between  the  wood 
frame  and  the  concrete.  Such  a  detail  is  illustrated  in  Fig.  54,  and  the 
security  of  the  joint  between  the  wood  frame  and  the  concrete  is  obtained 


Fig.  52. — Detail  of  window  construction. 
Reveal  molding  and  inside  trim 
placed  around  head  of  frame. 


&■**■* '-j^  **&*?■£ 

".    <*.  ■     -     «  ft:    <     ;  ■  %  y       --    '<  '* 

<  4  Jl    -.   '«.-.       +  „   ;    «• 


■Plaster 


-Trim 


Door 


Fig.    53-  -Separately    molded    sill    set    in       Fig.  54. — Detail  of  construction  for  door 
place.  frames  in  concrete  houses. 

[741 


by  casting  a  groove  in  the  concrete,  and  by  extending  the  outside  casing 
into  the  groove.  This  construction  is  shown  in  the  figure  at  a.  The  door 
frame  is  still  further  secured  and  made  tight  in  place  by  plugging  the  jamb 
and  nailing  under  the  stop  bead,  as  shown  at  b. 

An  interesting  detail  of  another  type  of  construction  for  a  door 
frame  is  that  illustrated  in  Fig.  55,  which  shows  a  plank  front  frame 
arranged  in  a  rebate. 

It  is  best  in  the  construction  of  concrete  houses  to  eliminate  cut- 
stone  work  as  much  as  possible,  and  to  form  the  sills  monolithic  with  the 
wall  or  cast  them  separately.     It  is  p.    .    . 

best  not  to  depend  for  the  threshold  Wafer- Fhoofmgj  /  ! 
upon  a  projection  formed  of  concrete, 
as  when  worn  it  is  difficult  to  replace. 
A  metal  or  hardwood  threshold  is 
superior.  In  the  best  work  this 
threshold  would  be  of  cast  brass, 
properly  secured  to  the  cement  sill. 
Of  course  there  is  no  reason  why 
bluestone,  granite  or  specially  cast 
concrete  stone  sills  should  not  be  set 

on  the  concrete  walls,  and  be  introduced  for  the  sills  of  door  openings 
where  there  is  apt  to  be  excessive  wear. 


frame 


Fig.  55. — Plank  frame  for  door  ar- 
ranged in  a  rebate. 


Concrete  Wall  Construction. — In  house  construction,  concrete  walls, 
and  especially  those  reinforced  with  steel  rods  or  bars  in  two  directions, 
have  some  advantages  over  walls  built  of  stone  or  brick. 

In  the  first  place,  concrete  walls  may  be  made  only  two-thirds  the 
thickness  of  brick  and  masonry  walls  and  still  be  of  equal  or  greater 
strength.  Since  such  walls  are  monolithic,  they  are  less  liable  to  buckle, 
and  the  junctions  at  corners  are  stronger;  besides,  the  work  over  the 
heads  of  window  and  door  openings  is  more  secure,  as  there  is  no  tendency 
for  arches  to  loosen  and  drop,  and  joints,  as  those  between  the  voussoirs, 
to  crack. 

Concrete  walls  are  good  non-conductors,  and  make  warm  winter 

[75] 


and  cool  summer  houses;  particularly  are  they  excellent  in  retaining  heat 
from  the  fact  that  there  is  less  likelihood  of  leakage  through  cracks  such 
as  is  the  rule  rather  than  the  exception  in  brick  and  masonry  walls.  Walls 
of  concrete  are,  when  properly  constructed,  much  more  likely  to  be  water 
and  weatherproof,  and  in  this  respect  are  an  improvement  over  brick  and 
stone  walls  of  rubble  masonry,  as  such  walls  are  ordinarily  constructed. 
In  this  fact  there  also  exists  one  marked  point  of  superiority  of  concrete 
for  wall  construction  as  compared  with  masonry  or  brick  walls,  which 
is  that  from  the  very  nature  of  the  material  a  concrete  wall  must  be  solid 
and  free  from  the  structural  defects  that  are  so  evident  in  walls  of  masonry 
where  the  workmanship  is  bad  or  even  fair. 

Strength  of  Concrete  Walls. — There  is  no  doubt  of  the  great  strength 
of  reinforced  concrete  walls,  but  careful  consideration  has  been  given  to 
this  part  of  reinforced  concrete  construction  in  framing  the  building  laws 
for  cities  of  the  first  class,  and  these  are  interesting,  as  they  indicate 
the  best  practice,  which  may  well  be  adhered  to  in  the  construction  of 
country  houses. 

The  New  York  city  regulations  governing  the  use  of  reinforced 
concrete  contain  the  following  interesting  and  instructive  paragraph : 

"Exterior  and  interior  bearing  and  enclosure  walls  of  reinforced 
concrete  supporting  floor  and  roof  loads  shall  be  securely  anchored 
at  all  floors,  and  of  such  thickness  that  the  compressive  stress  shall 
not  exceed  250  pounds  per  square  inch,  but  in  no  case  shall  the 
walls  be  less  than  8  inches  in  thickness.  The  thickness  of  such 
walls  shall  not  in  any  instance  be  less  than  ^V  °f  the  unsupported 
height." 

And  further  in  reference  to  the  reinforcement  of  concrete  walls  the 
law  states: 

"Steel  reinforcement  shall  be  placed  near  both  faces  of  the  wall, 
running  both  horizontally  and  vertically,  and  weighing  not  less 
than  Yi  pound  per  square  foot  of  wall." 

Method  of  Supporting  Floors. — The  best  practice  in  concrete  house 
construction  is  to  use,  in  conjunction  with  the  concrete  walls,  fire-proof 

I  76] 


Typical  sectional  form  for  concrete  wall  construction. 


Method  of  securing  window  frames  during  wall  construction. 
[77) 


Wall  recesses  for  timber  joist. 


Pouring  concrete  into  a  column  form. 
178) 


floors,  ordinarily  also  of  reinforced  concrete  construction.  When  such 
floors  are  used  they  become  monolithic  with  the  walls,  and  a  very  rigid 
and  secure  building  is  obtained  by  allowing  the  reinforcing  rods  of  the 
beams  to  interlace  with  those  of  the  walls. 

Should  wood  construction  be  used  for  the  floors  in  dwellings  where 
the  walls  are  of  concrete,  as  is  sometimes  done  in  the  smaller  houses,  the 


a  b 

Fig.  56. — Two  methods  of  setting  wooden  joist  in  concrete  walls. 

joist  may  be  set  and  cast  in  place,  or  else  be  supported  in  the  ways  il- 
lustrated in  Fig.  56  at  (a)  and  (b). 

The  objection  found  to  the  method  of  supporting  the  ends  of  the 
joists  or  floor  timbers  by  setting  them  and  casting  them  in  place  is  that 
when  the  ends  of  the  timbers  are  thus  confined  the  wood  is  liable  to  decay. 
They  should  always  set  in  a  pocket  somewhat  larger  than  their  dimen- 
sions, so  that  the  air  may  get  to  the  wood  and  prevent  dry  rot. 

The  manner  of  supporting  the  joists  or  floor  beams  shown  in  Fig.  56 

[79l 


at  (a),  is  good,  from  the  fact  that  the  wall  may  be  run  up  several  stories 
and  the  floors  rapidly  constructed  after  the  centering  for  the  walls  has 
been  removed.  By  arranging  the  iron  ties  and  embedding  their  ends  in 
the  concrete,  every  fourth  or  fifth  joist  may  be  used  to  tie  the  building 
together,  or  if  so  desired,  every  joist  may  be  tied  in.  One  advantage 
exists  here  in  that  the  ledge  makes  an  excellent  bearing  for  the  joist,  and 
is  also  very  convenient  for  sizing  the  joists  and  bringing  them  to  a  level. 
Joists  or  floor  beams  may  also  be  supported  in  a  very  secure  and  efn- 

■*■'.)  '>'>.-.'.  gBSSgSggBBg  5SSZ2  3SS3  SSS553  SS2SZ33 

*  V-  .->  +.i  «.•"'■"■*  •■*  «■.«  «-«i  .',:.  ••  ■<.«••<•  ■*  ■.'«•«  <»'.•»•«; 

-  J3  ;  /' ,  -v*4.'*  .1*1  •»•  >  >  iv  •     *>,:  *•«-  •"•  w. •■'■»  J  '-  * 


•r  -  *.■■».    :  '  k  A  .  ..J 


(a) 


ia  , .  . .     isr 


(6) 
Fig-  57- — Hollow  walls  fastened  together  with  copper,  galvanized  iron,  or  concrete  ties. 

cient  manner  by  using  wall  hangers,  as  shown  in  the  figure  at  (6).  These 
hangers  are  known  as  "Duplex  Concrete  Hangers,"  and  are  made  for 
2",  3"  and  4"  joists,  especially  for  concrete  construction,  though  any 
hanger  of  suitable  design  could  as  well  be  used. 

Both  of  the  methods  shown  in  the  figure  permit  all  of  the  ends  of  the 
joists  or  floor  timbers  to  be  well  ventilated. 

Hollow  Concrete  Walls. — As  any  dead  air  space  in  a  wall  or  floor 
of  any  material  is  most  excellent  on  account  of  the  insulation  it  provides 
in  case  of  either  heat  or  cold,  as  well  as  sound,  and  also  because  a  drier 
interior  wall  surface  is  obtained,  concrete  walls  so  cast  have  some  ad- 
vantages over  solid  concrete  walls.  The  best  construction  is  to  make 
the  two  walls  as  distinct  as  possible  and  to  provide  as  few  connections 

[80I 


between  the  two  walls  as  is  practical  to  insure  the  stability  of  both. 
In  fact  it  is  far  better  to  unite  the  two  walls  with  only  copper  or  galvan- 
ized iron  ties,  as  shown  in  Fig.  57  at  (a),  than  to  tie  them  together  with 
cross  walls  of  concrete  as  illustrated  at  (b).  Such  walls  as  the  latter  are 
costly,  and  somewhat  difficult  to  construct  unless  special  or  patented 
forms  or  centerings  are  used.  Generally  the  air  space  desired  may  be 
obtained  by  some  other  means,  such  as  a  veneer  lining  or  furring,  at  a 
considerably  less  cost  and,  withal,  greater  efficiency. 

Veneered,  Lined  and  Furred  Walls. — In  order  to  insure  against 
dampness,  and  more  especially  to  prevent  the  possibility  of  condensation 
on  the  inside  of  walls  of  concrete,  a  condition  which  is  hardly  likely  to 
occur  except  under  extraordinary  conditions  of  exterior  cold  and  great 


*  .*  t   ■*.  *  *  ..*...-  *• >  •  ♦  ■.-■  .•■  •*  »■  .■  «,■  A  ,j  •  ■  »■"  •  a  *  .«• 

Fig.  58. — Furring  inside  concrete  walls  with  hollow  brick,  plaster  block,  or  tile. 

interior  humidity,  and  also  to  provide  greater  insulation,  it  is  best  where 
the  expense  is  not  a  factor  in  the  problem  of  dwelling  house  construction 
to  veneer,  line  or  furr  the  walls  on  the  inside. 

A  good  practice  is  to  veneer  or  line  the  inside  walls  with  hollow 
brick,  plaster  block,  or  tile,  as  shown  in  Fig.  58.  A  method  equally 
efficient  is  to  furr  the  walls  on  the  inside  with  metal  lath  and  furring 
strips.  In  either  case  the  desired  air  space  is  obtained  without  in  any 
way  destroying  the  fireproof  properties  of  the  construction.  An  ex- 
cellent lining  for  concrete  walls  is  found  in  a  layer  of  cork,  which  may  be 
stuck  to  the  walls  with  cement,  and  which  readily  takes  plaster. 

Concrete  walls  8  inches  in  thickness,  painted  on  the  inside  with  a 
damp-proof  paint  proper  for  covering  concrete,  will  answer  every  purpose. 


Chapter  IV 
Operations  in  the  Field 


Workingman' s  Cottage,  Sage  Foundation  Homes  Co.  Grosvenor  Atterbury,  Architect 

The  huge  cored  slabs  for  walls,  floors,  roof  and  partitions  and  even  stairways 

are  precast  and  assembled  in  manner  shown. 


84 


Chapter  IV 
Operations  in  the  Field 

With  the  structure  satisfactorily  designed,  successful  construction  of 
a  building  of  any  material  is  dependent  upon  the  careful  selection  of  the 
component  materials  and  a  working  knowledge  of  how  to  combine  them 
properly.  The  wide  distribution  of  sand,  rock  and  gravel  (known  as 
the  aggregate)  and  the  extensive  use  of  concrete  have  increased  general 
knowledge  as  to  what  constitutes  good  materials  and  the  ability  to  do 
good  work.  Such  results  have  been  brought  about  by  following  definite 
methods  which  have  now  become  common  practice. 

Selection  of  Materials. — In  selecting  Portland  cement  always  secure  a 
brand  guaranteed  to  meet  the  requirements  of  the  standard  specifica- 
tions of  the  United  States  Government  or  those  of  the  American  Society 
for  Testing  Materials.  Portland  cement  may  be  had  in  cloth  sacks, 
paper  bags  or  wooden  barrels.  More  commonly  it  is  shipped  in  cloth 
sacks  with  an  allowed  rebate  for  the  return  of  empty  bags  in  good  con- 
dition. Each  bag  of  cement  weighs  94  pounds  net  and  four  bags  con- 
stitute a  barrel  of  376  pounds.  One  bag  of  loose  cement  is  practically 
equivalent  to  one  cubic  foot.  On  account  of  its  sensitiveness  to  moisture, 
Portland  cement  must  be  carefully  protected  from  dampness  at  all  times, 
even  when  piled  at  the  site  of  the  work. 

Sand  for  concrete  should  be  had  hard  and  clean  and  should  have 
grains  grading  in  size  from  %  inch  down.  Pit  and  stream  sands  are 
generally  of  good  quality,  but  drift  sand  is  usually  too  fine  of  grain  to 
make  good  concrete.  The  presence  of  dirt  can  easily  be  ascertained  by 
pouring  a  small  quantity  of  sand  into  a  pail  of  clear  water  or  by  rubbing 
a  portion  between  the  palms  of  the  hands.     A  practical  test  may  be  made 

[85] 


by  placing  a  four-inch  depth  of  sand  in  a  fruit-jar,  and  by  adding  water 
until  the  jar  is  within  one  inch  of  full  and  by  shaking  the  contents  vigor- 
ously. If,  after  the  water  has  again  become  clear,  there  is  a  layer  of  mud 
more  than  one-fourth  inch  in  thickness,  the  sand  should  not  be  used 
without  first  washing. 

The  most  suitable  stone  for  crushed  rock  is  one  which  is  clean,  hard, 
breaks  with  sharp  angles  and  to  which  mortar  easily  adheres.  Trap, 
granite  and  hard  limestone  are  among  the  best.  The  use  of  shale,  slate, 
and  very  soft  limestones  and  sandstones  should  be  avoided.  The  crushed 
rock  should  be  screened  only  sufficiently  to  remove  the  fine  dust.  The 
maximum  size  of  stone  allowable  is  often  dependent  upon  the  thickness 
of  the  object  to  be  molded.  It  is  common  practice  to  fix  the  extreme 
limit  at  \%  inch  in  diameter. 

Bank-run  gravel,  just  as  dug  from  the  pit  or  taken  from  the  stream 
bed,  seldom  runs  even  and  rarely  has  the  proper  proportions  of  sand  and 
pebbles  for  making  the  best  concrete.  An  ideal  pit  gravel  is  40  per  cent, 
sand.  Since  there  is  generally  too  much  sand  in  proportion  to  the 
pebbles,  it  is  advisable  and  economical  to  screen  the  sand  from  the  peb- 
bles and  then  to  remix  them  in  the  correct  proportions.  As  a  general 
rule,  pebbles  larger  than  \x/±  inch  in  diameter  are  discarded;  all  material 
smaller  than  l/±  inch  is  considered  sand.  Gravel  should  contain  no 
rotten  stone  and  should  be  clean. 

Depending  on  the  character  of  the  particles,  sand,  crushed  rock  and 
gravel  vary  in  weight  from  100  to  no  pounds  per  cubic  foot. 

For  fire-proofing  and  for  various  other  purposes  requiring  low 
stresses,  cinder  concrete  is  frequently  used.  The  cinder  should  consist 
of  hard,  clean,  vitreous  clinker  free  from  sulphides,  unburned  coal  and 
ashes.  A  clean  cinder  will  not  discolor  the  palms  of  the  hands  when 
rubbed  between  them. 

The  water  used  in  mixing  the  concrete  should  be  clean  and  free 
from  oil,  alkali  and  vegetable  matter. 

Proportioning  and  Mixing. — The  proper  proportion  for  combining 
the  Portland  cement  and  the  aggregate  is  dependent  upon  the  quantity  and 

[86] 


character  of  the  materials  and  the  purpose  for  which  the  resulting  con- 
crete is  intended.  For  reinforced  and  damp-proof  concrete  that  propor- 
tion is  desirable  which  produces  the  densest  concrete  possible.  Under  other 
conditions  only  sufficient  cement  is  used  to  develop  the  strength  required 
of  the  concrete.  For  reinforced  and  damp-proof  concrete,  a  1 .2:4  mix  is 
commonly  employed.  Where  compressive  strength  alone  is  a  requisite, 
the  concrete  is  frequently  proportioned  1:2^:5.  For  massive  founda- 
tions, a  1:3:6  concrete  may  be  used.  In  such  proportions,  the  first 
numerical  term  refers  to  the  parts  of  Portland  cement,  the  second  to 
the  parts  of  sand  and  the  third  to  the  parts  of  crushed  rock,  screened 
gravel,  or  other  coarse  aggregate.  The  proportions  are  based  on  meas- 
urements by  volume  in  which  a  bag  of  cement  is  considered  one  cubic 
foot.  If  pit  gravel  is  used,  although  the  saving  in  cement  will  usually 
more  than  compensate  the  cost  of  screening  and  remixing,  similar  pro- 
portions are  adopted  in  which  the  second  or  sand  term  is  dropped.  Such 
proportions  then  read  1  4,  1 :5  and  1 :6.  Cinder  concrete  is  usually  made 
in  the  proportion  1  part  cement  to  2\  parts  sand  to  5  parts  cinders. 
Oh  large  work,  and  where  the  determination  of  the  exactly  correct  pro- 
portions is  expedient,  the  voids  in  the  sand  and  stone  are  determined  by 
saturation  with  water  or  by  specific  gravity.  With  the  proportion  of 
voids  thus  carefully  ascertained,  there  is  generally  used  an  excess  of  5 
to  10  per  cent,  of  cement  over  the  voids  in  the  sand  and  a  5  per  cent, 
excess  of  sand  over  the  voids  in  the  stone. 

In  making  a  batch  of  concrete  the  amount  of  each  material  required 
should  be  actually  measured  by  volume,  otherwise  concrete  entirely 
homogeneous  in  texture  and  appearance  can  not  well  be  produced. 
Since  a  bag  of  Portland  cement  (loose)  is  equivalent  to  one  cubic  foot,  for 
convenience  all  measurements  should  be  based  on  the  cubic  foot  as  the 
unit.  As  a  means  of  measuring,  a  bottomless  box,  or  a  device  equally 
exact,  should  be  employed.  The  sizes  of  measuring  boxes  are  depend- 
ent upon  the  amount  of  concrete  to  be  mixed  in  each  batch. 

The  materials  can  be  thoroughly  mixed  into  concrete  either  by  hand 
or  by  machine.  The  method  selected  is  dependent  entirely  upon  con- 
ditions.    Where  the  work  is  of  such  a  character  and  size  as  to  war- 

[89] 


rant  the  investment,  much  faster  progress  can  be  made  by  using  a  ma- 
chine mixer.  The  machine  should  be  of  such  a  type  as  to  insure  uni- 
form mixing  of  the  materials  throughout  the  mass  of  concrete.  There 
are  many  such  machines  on  the  market  and  the  merits  of  each,  as  adapted 
to  the  user's  particular  needs,  should  be  carefully  studied. 

For  work  of  moderate  magnitude,  measuring  boxes  of  convenient 
size  are  specified  in  Table  I. 

Table  1. — Showing  Quantities  of  Materials  and  Approximate  Resulting 
Amount  of  Concrete  for  Two-bag  Batch,  Using  Sand  and  Stone 


Propor- 
tions by 
Parts 

Two-bag  Batch 

Kind  of  Concrete 

1 

B> 

0 
s 
to 

Materials 

Con- 
crete* 

Size  of  Measuring 
Boxes.     Inside 
Measurements 

Mixture 

5 

3 

e 

3 

3 

8* 

Water  in 
Gallons 
for  Med- 
ium Wet 
Mixture 

Sand 

Stone 

or 
Gravel 

Bags 

Cubic 
Feet 

Cubic 
Feet 

Cubic 
Feet 

Gallons 

1:2:4  concrete. . . . 
1:2^:5  concrete.. 
1:3:  6  concrete. .  .  . 

1 
1 
1 

2 

2K 
3 

4 
5 
6 

2 
2 

2 

3H 
4K 
53A 

lA 
9A 

%A 
10 
12 

2'X2' 
2'  X  2}4' 

11A" 
2'x3' 

11K" 

2'XA' 

uA" 

2'x5' 
2'x6' 

\\A" 

10 
12K 
I3# 

There  are  several  slightly  different  and  entirely  satisfactory  meth- 
ods of  mixing  concrete  by  hand.  When  sand  as  a  fine  aggregate  is 
used  with  a  coarse  aggregate  (such  as  crushed  rock,  screened  gravel, 
cinders,  etc.),  the  sand  is  carefully  measured  and  the  entire  quantity 
required  for  one  batch  of  concrete  is  spread  out  in  a  thin,  oblong  shape 
upon  a  smooth,  tightly  jointed  mixing  board.  Upon  the  sand  is  scattered 
evenly  the  full  amount  of  Portland  cement  needed.  The  two  materials 
are  then  mixed  dry  by  shoveling,  with  the  laborers  working  opposite 

*  Amount  of  concrete  resulting  is  only  roughly  approximate.  In  estimating  quan- 
tities use  Table  2,  page  92. 

[90] 


each  other  in  pairs.  They  turn  the  cement  and  sand  with  a  dragging 
stroke  which  is  very  effective  in  mixing  the  materials.  During  this 
operation  a  helper  aids  the  mixing  by  using  a  garden-rake.  The  turning 
continues  until  the  cement  and  sand  no  longer  show  in  streaks  and  the 
mass  has  a  uniform  color. 

The  mixture  is  again  spread  out  in  its  original  oblong  shape  and  the 
measured  full  amount  of  stone  or  other  coarse  aggregate  is  scattered 
evenly  over  it.  About  one-half  to  two-thirds  of  the  required  amount  of 
water  is  sprinkled  over  the  stone,  after  which  the  mass  is  turned.  The 
concrete  is  thrown  into  a  ridge,  is  cut  open  to  a  crater  shape,  and  the 
remainder  of  the  water  is  added.  Turning  is  continued,  and  a  little 
water  added  to  the  dry  spots  until  the  mass  is  thoroughly  mixed. 

For  bank-run  gravel  (or  other  material  in  which  the  fine  and  coarse 
aggregate  are  not  separated)  the  method  of  mixing  is  slightly  different. 
One-half  of  the  total  aggregate  required  is  spread  out  in  oblong  shape, 
the  full  amount  of  Portland  cement  is  scattered  over  it,  and  the  remainder 
of  the  aggregate  is  added.  The  materials  are  turned  dry  until  they  are 
thoroughly  mixed,  when  the  mass  is  cut  open  and  water  added  in  the 
same  manner  as  described  above  when  sand  and  crushed  rock  are  used. 

The  amount  of  water  necessary  to  a  batch  of  concrete  is  dependent 
upon  the  character  and  condition  of  the  aggregate  and  the  consistency 
required  of  the  concrete  for  the  purpose  and  for  the  manner  in  which 
it  is  to  be  used.  When  possible,  and  especially  for  reinforced  construction, 
it  is  advisable  to  use  that  consistency  commonly  known  as  mushy,  in 
which  state  the  concrete  is  sufficiently  wet  that,  when  being  transported 
from  the  mixer  to  the  work  in  buckets  or  in  wheelbarrows,  its  surface 
naturally  becomes  smooth  and  level.  With  all  things  equal,  mushy 
wet  concrete  is  most  dependable  for  completely  filling  all  space  in  the 
forms,  for  securing  a  perfect  bond  with  the  metal  reinforcing,  and  for 
producing  a  very  dense  concrete. 

For  certain  effective  surface  treatments  and  for  detailed  ornamental 
castings  a  dry  concrete  is  frequently  used.  The  amount  of  moisture 
required  is  a  variable  quantity.  At  least  sufficient  water  should  be  used 
to  give  the  material  the  plasticity  common  to  molding  sand.     For  mas- 

(91] 


sive  work  dry  concrete  should  be  wet  enough  to  flush  mortar  slightly  to 
the  surface  under  heavy  tamping.  Dry  concrete  attains  a  working 
strength  more  quickly  than  wet  concrete,  and  the  forms  may  be  removed 
sooner,  but  ultimately  the  wet  mix  surpasses  it  in  strength. 

In  casting  ornamental  concrete,  and  for  other  purposes,  a  mortar  is 
frequently  required.  Sand  is  generally  chosen  as  the  fine  aggregate,  though 
stone  screenings  of  various  kinds  are  often  used.  The  proportions  are  de- 
pendent upon  the  sizes  of  the  particles  in  the  aggregate.  In  general  I  part 
of  cement  is  used  to  i^  or  2  parts  of  fine  aggregate.  Mortars  too  rich  in 
cement  are  liable  to  check  and  thus  injure  the  appearance  of  the  surface. 

At  the  greatest,  not  more  than  thirty  minutes  should  elapse  between 
the  mixing  of  the  concrete  and  the  depositing  of  it  into  permanent  posi- 
tion. The  methods  of  handling  the  concrete  between  the  mixer  and  the 
forms  vary  with  the  size  of  the  work.  On  large  construction,  hoists  are 
used  in  connection  with  distributing  spouts.  For  smaller  structures 
derricks,  wheelbarrows,  and  buckets  are  the  usual  means  of  conveyance. 

Estimating  Quantities  of  Materials  Needed. — For  estimating  the 
quantities  of  materials  needed  for  any  structure,  Tables  2  and  3  will  be 
of  considerable  service.  In  making  up  the  estimate,  compute  the  total 
cubic  feet  of  mortar  or  concrete  required  and,  for  the  barrels  of  cement 
and  cubic  yards  of  sand  and  stone,  multiply  this  total  by  the  decimal 
figure  under  each  respective  heading.  These  tables  are  based  on  ordi- 
nary sand  and  on  average  conditions  of  45  per  cent,  voids  in  broken  stone 
with  the  dust  screened  out. 


Table  2. — Estimating  Quantities  of  Materials  for  Mortar 


Mixture 


1:2. . 

l:2K 


92 


Quantities  of  Materials  in  One  Cubic 
Foot  of  Mortar 


Cement 


Sand 


Barrel 
0.1481 
0.1239 
0.1052 

Cubic  Yard 
0.031 1 
0.0344 
0.0370 

Table  3. — Estimating  Quantities  of  Materials  for  Concrete 

Mixture 

Quantities  of  Materials  in  One  Cubic  Foot  of 
Concrete 

Cement 

Sand 

Stone  or  Gravel 

1:2:4  concrete  

Barrel 
0.058 
0.048 
0.041 

Cubic  Yard 
0.0163 
0.0170 
0.0174 

Cubic  Yard 

0.0326 
0.0341 
0.0348 

1 : 2}/2 : 5  concrete 

1:3:6  concrete 

To  illustrate  the  manner  of  using  these  tables,  assume  that  25  cubic 
feet  of  1 :  2  mortar  and  850  cubic  feet  of  concrete  are  required  for  a  bunga- 
low. Of  this  concrete,  90  cubic  feet  of  a  1 :2^:5  mix  are  needed  for  the 
footings  and  foundations  and  the  remaining  760  cubic  feet  of  a  1 :2  4.  mix 
for  cellar  and  house  walls,  etc. 

ESTIMATE  FOR  BUNGALOW 

Cement  for  1:2  mortar 25  X  0.1239     3.10  bbls. 

Sand  for  1 :  2  mortar 25  X  0.0344     °-86  cu.  yds. 

Cement  for  1 :  2]A:  5  concrete 90  X  0.048       4.32  bbls. 

Sand  for  1:2^:5  concrete 90  X  0.0170     1.53  cu.  yds. 

Stone  for  1 :  2}4:  5  concrete 90  X  0.0341     3.07  cu.  yds. 

Cement  for  1:2:4  concrete 760  X  0.058     44.08  bbls. 

Sand  for  1:2:4  concrete 760  X  0.0163   I2-39  cu.  yds. 

Stone  for  1:2:4  concrete 760  X  0.0326  24.78  cu.  yds. 

Formwork  and  Centering. — The  formwork  and  centering  for  reinforced 
concrete  construction,  while  it  is  purely  falsework,  which  is  taken  down, 
removed  and  is  no  part  of  the  finished  structure,  enters  considerably  into 
the  cost  of  any  concrete  building. 

To  illustrate  the  great  percentage  to  the  cost  of  construction  the  form 
work  and  centering  bear  to  the  finished  structure,  it  might  be  stated  that 
reinforced  concrete  for  house  construction  in  place  is  worth  about  $21.00 
a  cubic  yard  for  the  usual  wall  and  floor  construction.  This  cost  is, 
roughly,  divided  equally  between  the  concrete,  the  steel,  and  the  form  and 
centering,  the  cost  of  each  being,  approximately,  $7.00  for  every  cubic 
yard  of  concrete  poured. 

This  cost  shows  how  important  it  is  that  the  formwork  and  centering 
should  be  of  such  a  design  that  it  may  be  economically  constructed,  and, 

[93l 


at  the  same  time,  produce  well  molded  work.  It  is  not  sufficient  that 
the  formwork  shall  be  smooth,  for  unless  care  is  taken  in  its  construction 
and  support  the  finished  work  will  show  sagged  floor  slabs,  beams  and 
girders,  posts  and  piers  out  of  plumb,  and  floor  members  twisted  and 
warped. 

The  strength  "and  accuracy  with  which  form  construction  must  be 
designed  and  executed  cannot  be  too  forcibly  brought  to  mind,  especially 
where  cast  concrete  is  a  feature  of  exterior  treatment  and  architectural 
decoration  of  a  building.  Nothing  can  look  worse  than  brackets,  mutuals 
or  pilaster  caps  which,  while  otherwise  well  wrought,  are  placed  out  of 
plumb  due  to  carelessness  in  placing  the  forms  and  in  supporting  them. 

Concrete  constructors,  realizing  the  importance  of  cheap  forms, 
have  devised  and  patented  many  particular  ideas  of  more  or  less  merit. 
In  form  and  centering  construction,  however,  like  other  structural  evolu- 
tions, there  has  been  a  "survival  of  the  fittest,"  and  in  nearly  all  instances 
the  patented  forms,  due  to  their  costliness  and  lack  of  adaptability  to 
particular  operations  of  construction,  have  not  been  generally  used. 
Forms  of  simple  design,  so  arranged  as  to  be  readily  put  together  and 
taken  down,  have  been  almost  standardized  where  concrete  construc- 
tion has  been  carried  on  extensively. 

Built-up  Form  Construction  for  Floors. — The  several  types  of  form 
construction  may  be  generally  classified  according  to  the  manner  in  which 
they  are  built,  as  "built-up,"  "unit  panel  construction,"  and  "constructive 
formwork." 

In  the  first  type,  the  beams  and  girders  of  the  floor  construction  are 
formed  in  the  concrete  by  building  up  wooden  troughs  having  the  size 
and  shape  of  the  beams  and  girders,  properly  supporting  these  upon 
suitable  uprights  well  braced,  and  covering  the  spaces  between  the  beams 
and  girders  with  battened  panel  sections  supported  upon  joists  or  ribs 
resting  upon  ledger  boards  nailed  to  the  sides  of  the  beam  and  girder 
form. 

This  type  of  form  construction  for  concrete  floors,  where  beams, 
girders  and  slabs  occur,  has  come  into  common  use,  and  a  working  draw- 

194] 


ing  giving  the  usual  sizes  of  the  pieces  used  in  the  construction  of  these 
forms  is  given  in  Fig.  59. 

Unit  Panel  Construction. — In  the  second  type,  the  unit  panel  con- 
struction, the  panel  formed  by  the  beams  and  girders  is  made  up  in  the 
form  of  a  box,  which,  when  inverted  and  properly  supported  upon  the 


w  Preset/  Jy/?  />//7<?( 


2x6 "  feZ/m  P/he 
7(?/7rf6/e  &  6 wore 


Fig-  59- — Details  of  forms  used  in  built  up-construction. 

bottom  boards  of  the  beams  and  girders,  makes  up  the  side  forms  for 
these  structural  members,  and  also  provides  a  centering  for  the  slabs. 

These  panel  forms  are  sometimes  made  in  sections,  so  as  to  be  col- 
lapsible, as  shown  in  Fig.  60.  The  operation  of  the  form  is  explained  by 
the  note  in  the  illustration. 

[95] 


As  the  unit  type  of  form  construction  is  used  especially  where  there 
are  a  great  number  of  unit  panels  of  the  same  size,  they  would  not  be  so 
practical  for  individual  house  construction,  though  they  could  well  be 
used  if  a  number  of  houses  of  the  same  plan  were  to  be  built,  as  in  an 
operation. 


Constructive  Forms. — In   the  third   type  of  form   construction  an 
effort  is  made  to  minimize  the  cost  of  centering  by  incorporating  in  the 


Piece  nedaed  m  place .,  when    s>upporf& 
jre  knocked  down   jnd  we<d<ie£>  re/rxpyea 
form    m&u  Jje    co/Up&ed 

Fig.  60. — Unit  panel  forms  made  in  collapsible  sections. 

actual  concrete  construction  a  means  by  which  the  sides  of  the  beams  and 
girders,  or  supporting  members,  can  be  formed,  the  space  filled,  and  a 
saving  in  more  costly  material  accomplished. 

This  type  of  form  construction  is  emphasized  in  what  is  known  as 
"Hollow-Tile"  and  "Joist  Construction,"  and  in  such  constructions 
as  "Ferro-Dome"  and  "Corr-Tile."  In  the  Ferro-Dome  construction 
the  stamped  steel  boxes,  when  properly  spaced  upon  supports,  with  flat 
boards  for  the  bottom  of  the  intersecting  beams,  form  a  mold  for  the  sides 
of  the  beams,  as  shown  in  Fig.  61.     Sometimes,  as  in  the  Corr-tile  con- 

[96] 


structioh  shown  in  Fig.  62,  instead  of  these  metal  forms,  square  blocks 
of  terra-cotta  are  used,  with  flanges  and  channel  tile,  making  a  complete 
form  for  intersecting  beams;  thus  all  that  is  needed  for  constructing  the 
work  is  a  flat  centering  properly  supported  on  studding. 


Fig.  61. — Example  of  Ferro-Domc  construction. 

Various  kinds  of  patented  forms  have  been  devised  which  are  sup- 
posed to  have  the  economical  advantage  of  being  adjustable  to  any  length 
of  span,  and  so  arranged  that  by  spreading  them,  different  widths  of  beam 
could  be  obtained.  It  is  considered  that  by  the  use  of  such  forms  their 
cost  was  practically  made  up 
on  the  first  job  for  which 
they  were  used,  and  that  the 
cost  of  the  form  construction 
on  subsequent  work  was  re- 
duced to  the  mere  expense 
of  hauling  the  forms  to  the 
site  and  placing  them  upon 

the  proper  centering,  with  a  small  percentage  of  loss  due  to  deterioration. 
Such  form  work  for  floor  construction  in  house  work  is  hardly  practical. 


Fig.  62. — Example  of  Corr-tile  construction. 


Forms  for  Wall  Construction. — In  the  construction  of  concrete  walls 
two  kinds  of  wooden  forms  are  used — namely,  those  which  are  constructed 

7  (97  ) 


to  cast  an  entire  story  height  of  wall,  and  those  which  are  arranged  to  build 
the  wall  in  sections  of  two,  three,  four,  or  five  feet  in  height. 

The  former  method  requires,  of  course,  the  most  lumber  and  car- 
pentry labor,  but  it  is  the  most  expeditious,  while  by  the  use  of  the  latter, 
or  sectional  forms,  the  cost  of  the  form  construction  is  reduced  to  a 
minimum,  but  the  work  proceeds  much  more  slowly. 

Besides  those  forms  of  lumber  made  up  by  carpenters  on  the  job, 
there  are  several  types  of  patented  forms  which  are  usually  of  the  sec- 


Fig.  63. — Typical  example  of  form  work  in  one-story  wall  construction. 

tional  type,  and  are  so  arranged  with  units  of  different  lengths  and  corner 
units,  as  to  allow  a  wall  of  any  length  or  plan  to  be  built. 


Forms  for  the  Construction  of  a  Story  Height  of  Wall. — The  arrange- 
ment and  construction  of  the  formwork,  where  a  story  height  of  wall 
is  to  be  placed  at  one  time,  is  shown  in  Fig.  63.  With  this  type  of  form- 
work  for  molding  concrete  walls,  the  one  side  of  the  form,  as  at  a  a,  must 


be  built  first,  either  upright  or  on  the  ground  and  raised,  and  then  se- 
curely braced  to  hold  the  side  plumb  and  true.  The  uprights,  as  at 
b  b,  may  be  3"  x  4",  or  preferably  2"  x  6"  yellow  pine,  spaced  not  further 
apart  than  24  inches  from  center  to  center.  The  sheathing  nailed  to  the 
uprights  may  be  either  \  x  2^"  face  tongued  and  grooved  yellow  pine 
flooring,  or  else  1"  x  12"  sap-pine  boards  dressed  on  one  side.  It  is  not 
necessary  that  the  back  braces,  at  c  c,  be  of  any  more  strength  than  enough 
to  hold  the  form  in  position  and  secure  it  against  wind  pressure,  because 
both  sides  of  the  form  must  be  tied  together  to  resist  the  pressure  of  the 


Fig.  64. — Spacers  for  reinforcement. 


wet  concrete.  It  would  not  be  practicable  or  economical  to  provide 
sufficient  back  braces  to  resist  the  bulging  or  buckling  effects  due  to  this 
cause. 

When  one  side  of  the  form  has  been  constructed  in  this  manner, 
the  other  side  may  be  built  and  placed,  being  braced  in  position;  before 
the  sheeting  boards  are  put  on,  the  steel  reinforcement  should  be  put 
in  position  and  secured  to  the  side  of  the  form  first  erected.  The  best 
way  to  fasten  and  place  the  steel  is  to  provide  looped  spacers,  as  shown 
in  Fig.  64,  through  which  the  vertical  rods  may  be  passed,  and  which 

[99] 


are  so  arranged  as  to  be  secured  to  the  back  form  with  staples.  These 
also  form  a  bearing  or  support  to  which  the  horizontal  reinforcement 
can  be  wired. 


Method  of  Tying  and  Separating  the  Sides  of  Forms. — The  braces 
shown  in  Fig.  63  are  only  intended  to  hold  the  two  sides  of  the  forms 
vertical  and  the  mass  of  the  wet  concrete  contained  between  them  in  a 
plumb  and  secure  manner  until  the  concrete  has  set.  It  is  never  con- 
sidered good  practice  to  attempt  to  brace  both  sides  of  the  forms  for  a 
wall  so  strongly  and  at  such  frequent  intervals  as  to  exclude  the  necessity 

of  other  ties  between  the  two  sides. 
Usually  wire  ties  or  bolts  are  used 
to  hold  in  the  sides  of  the  forms 
and  prevent  them  from  bulging 
on  account  of  the  hydrostatic 
pressure  of  the  wet  concrete. 
When  the  ties  or  bolts  are 
drawn  up  it  is  difficult  to  regu- 
late the  tension  so  that  the  forms 
will  not  be  either  bulged  or  pulled 
in  and  otherwise  warped  and  dis- 
torted. To  avoid  this  trouble 
some  means  is  employed  to  keep 
the  sides  of  .the  wall  forms  at  the 
same  distance  apart  when  the 
bolts  or  wire  ties  are  drawn  up. 
The  usual  methods  of  tying  the  sides  of  the  forms  together,  and  ar- 
rangements for  separating  them  at  proper  distances,  are  shown  in  Figs. 
65,  66,  and  67. 

In  Fig.  65  is  shown  a  method  which  meets  with  much  favor  on 
account  of  its  cheapness  and  the  convenience  with  which  the  materials 
may  be  obtained.  The  separator  a  consists  of  a  small  stick  of  wood 
smoothed  and  accurately  cut  to  length,  while  close  to  it  is  placed  the  wire 
tie  &,  of  No.  18  gauge  soft  iron.     This  is  formed. in  U-shape,  passed  around 


Fig.  65. — A  common  method  of  bracing  and 
tying  wall  forms. 


the  upright  c,  through  holes  in  the  forms,  and  twisted  around  the  upright 
d.  The  proper  tension  is  obtained  by  twisting  the  wires  with  a  bar,  as 
at  e.  Sometimes,  owing  to  the  fact  that  the  wire  cuts  into  the  wood  of 
the  uprights,  a  small  metal  plate  or  another  stick  of  wood  is  inserted  be- 
tween the  wire  tie  and  the  upright. 

When  wooden  separators  of  this  kind  are  used  they  are  generally 
pushed  through  the  concrete  while  the  work  is  still  "green";  or,  at  least, 
before  it  has  set  hard.     When  the  forms  are  removed  the  ends  of  the  wire 


Fig.  66. — The  use  of  the  hook  bolt  as  a  substitute  for  wire  ties. 


ties  are  cut  off  and  the  work  is  finished  by  filling  the  holes  left  in  the  con- 
crete when  the  wooden  separators  are  driven  out. 

One  of  the  disadvantages  of  using  the  wire  ties  and  cutting  them  off 
in  this  manner  is  due  to  the  fact  that  some  of  the  ends  will  be  exposed, 
will  rust,  and  this  iron  rust  running  down  the  surface  of  the  wall  will 
cause  unsightly  stains. 

This  difficulty  can  be  obviated  by  the  use  of  a  hooked  bolt,  illustrated 
in  Fig.  66.  The  bolt  a  is  formed  with  a  hooked  end  to  fit  over  the 
upright  as  at  b;   it  passes  through  the  two  forms  and  is  brought  to  the 

[  ioi  1 


proper  tension  by  the  use  of  a  bar,  an  iron  plate  washer  and  a  wrench  nut, 
as  shown  at  c.  In  this  construction  the  bolt  is  withdrawn  before  the  con- 
crete has  completely  hardened,  though  the  bolts  may  be  loosened  by 
partially  removing  them,  or  by  turning  them  while  the  concrete  is  setting 
up.  In  this  way  they  may  be  more  readily  withdrawn  when  the  forms 
are  taken  down.  Sometimes  instead  of  the  wooden  separator,  an  iron 
pipe   separator  is  slipped  over  the  bolts  and  left  in  the  concrete  wall. 


Fig.  67. — A  practical  type  of  wall  form  separator. 


These  pipe  separators  are,  however,  costly,  and  have  the  same  objection 
as  the  wire  ties  with  regard  to  rusting  at  the  ends. 

A  good  wall  form  separator  is  that  known  as  the  "McCarty  Con- 
crete Separator."  This  is  simply  a  spool  or  cylinder  of  concrete  with  a 
hole  through  the  center  for  the  tie-bolt,  molded  to  the  length  required  for 
the  thickness  of  the  wall  and  left  embedded  in  the  concrete.  Being  ce- 
ment, it  becomes  incorporated  with  the  concrete  of  the  wall,  and  is  not 
subject  to  the  objection  found  in  metal  separators.  This  separator  with 
the  tie-bolt  is  illustrated  in  Fig.  67. 

[  102  1 


Fig.  68. — A  clever  device  used  in  connection  with 
wire  ties 


A  clever  device  which  can  be  used  with  wire  ties,  and  by  which  the 

ends  of  the  wire  ties  can  be 

covered  with  the  concrete  on 

the  surface  of  the  wall  after 

the  forms  have  been  removed, 

is  illustrated  in  Fig.  68.     This 

device  is  clearly  shown  in  the 

figure,  and  its  use  in  conjunc- 
tion with  the  wire  tie,  or  with 

a  rod  tie  with  hooked  ends, 

is  shown   in   the  illustration. 

When    the    forms  are    to  be 

taken  down  the  wedge  at  d  is 

knocked  out  and  the  forms  removed;    then  the  device  may  be  released 

from  the  wire  or  hooked  tie  by  knocking  over  the  end  of  the  hooked  lever, 

as  at  b,  thus  releasing  the  de- 
vice from  the  tie.  In  this  way 
the  ends  of  the  tie  do  not  come 
closer  to  the  surface  than  one- 
half  or  three-quarters  of  an 
inch,  and  are  covered  by  the 


concrete.  The  hole  left  in  the 
surface  of  the  wall  by  the  re- 
moval of  the  device  can  be 
filled  by  plastering  or  grouting. 

Panel  or  Sectional  Wall 
Forms. — Where  the  wall  is 
to  be  constructed  in  sections 
three  or  four  feet  high,  the 
form  work  becomes  compara- 
tively simple.  A  good  arrange- 
ment for  the  construction  of 
concrete  walls  in  sections  is  to  use  battened  panels,  as  at  a  a  in  Fig.  69, 

[  103  ] 


Fig.  69. — Panel  or  sectional  wall  forms. 


supported  and  braced  by  the  uprights  b  b,  made  up  of  two  pieces  of 
2"  x  6"  timber,  held  together  by  separators  at  the  end,  as  at  c  c;  when 
braces  of  this  kind  are  used  bolts  can  be  placed  in  any  position,  and  the  sep- 
arator at  the  top  holds  the  braces  together  as  a  yoke.  The  braces  are  suffi- 
ciently long  to  grip  that  portion  of  the  wall  already  constructed,  and  in 
this  way  the  form  construction  for  the  portion  of  the  wall  to  be  built 
is  held  plumb  and  secure  over  the  finished  wall.     The  tie-bolts  may  be 


Fig.  70. — "Sullivan  Pressed  Steel  Plank-Holders. 


oiled  or  soaped  so  that  they  can  be  more  readily  withdrawn  from  the 
concrete. 

Where  there  is  much  wall  to  construct,  or  where  the  contractor  can 
use  the  braces  for  a  number  of  operations,  they  may  be  made  of  channel 
or  angle  irons  placed  back  to  back,  held  together  with  separator  plates 
and  rivets.  These  are  much  more  costly,  of  course,  than  the  wooden 
braces,  and  somewhat  heavier  to  handle. 

Another  method  of  constructing  concrete  walls  in  sections  is  illus- 
trated in  Fig.  70,  which  shows  the  use  of  what  is  known  as  the  "Sullivan 

[104] 


Pressed  Steel  Plank-Holders."  By  means  of  these  the  form-boards  are 
interlocked  at  the  corner  and  together,  and  they  also  act  as  a  washer  and 
grip  for  the  tie-bolts;  wire  ties  may  be  used  with  them  as  well  as  bolts. 

Forms  for  Hollow  Wall  Construction. — Hollow  walls  built  of  concrete 
have  been  used  for  house  construction  to  some  extent.  The  advantage  of 
a  hollow  concrete  wall  consists  in  the  dead-air  space  contained  between  the 
inside  and  the  outside  wall,  which  insulates  the  building,  tending  to  make 
it  cool  in  summer,  and  allowing  it  to  retain  the  heat  in  winter.     Concrete 


Fig.  71. — Wooden  forms  for  hollow  wall  construction. 


is,  however,  such  an  excellent  non-conductor,  and  solid  concrete  walls  are 
so  much  superior  to  brick  and  stone  walls  with  regard  to  their  ability  to 
prevent  radiation,  that  the  additional  expense  required  to  build  hollow 
walls  of  concrete  is  hardly  warranted. 

Forms  for  the  casting  of  hollow  concrete  walls  are  necessarily  com- 
plicated, and  are  particularly  so  when  attempts  are  made  to  construct 
them  with  wooden  forms.  It  is  only  possible  to  construct  hollow  walls 
by  means  of  sectional  forms  arranged  to  cast  two  or  three  feet  of  the  wall 
at  a  time.     Fig.  71  illustrates  a  type  of  wooden  form  construction  that 

[105] 


can  be  used  where  a  hollow  wall  is  desired.  The  outside  forms  are  of  the 
usual  battened  type,  braced  by  the  slotted  wooden  braces  yoked  at  the 
top,  as  shown  at  a  a.  The  bars,  at  b  b,  which  support  a  wooden  core  box, 
rest  upon  the  top  of  the  battened  forms  for  molding  the  outside  of  the 
wall.  This  core  box  is  so  arranged  that  it  can  be  wedged  out  to  the 
required  width  by  means  of  cleats  or  wedges,  and  after  the  concrete  has 
been  cast  these  cleats  or  wedges  are  released  and  the  core  box  is  slightly 
collapsed,  thus  allowing  it  to  be  withdrawn. 

Many  devices  can  be  gotten  up  which  will  permit  the  collapsing  or 
slight  reduction  in  size  of  the  core  box,  arranged  to  operate  by  the  use  of 
wedges  or  keys  driven  into  place,  or  released  by  a  blow  from  a  hammer. 

Good  results  at  reasonable  cost  in  the  construction  of  hollow  concrete 
walls  can  only  be  obtained  by  spending  much  care  and  thought  upon  the 
construction  of  the  core  box,  and  where  there  is  much  work  of  this  kind 
to  be  done  it  would  be  better  to  use  specially  designed  metal  forms  for 
the  construction  of  hollow  walls.  There  are  several  types  of  patented 
hollow-wall  forms  on  the  market  which  can  be  used  economically  where 
several  buildings  are  to  be  built. 

Patented  Steel  Forms. — Steel  forms  made  up  in  units,  with  special 
devices  for  clamping  the  several  units  together,  have  been  developed 
and  used  to  a  considerable  extent.  It  is  impossible  here  to  describe 
at  length  the  several  types  of  patented  sectional  steel  and  steel-lined 
forms.  One  of  the  most  recent  types  of  steel  forms  for  wall  work  is  illus- 
trated in  Figs.  72  and  73.  The  former  shows  in  detail  the  unit  sections 
of  the  forms  and  the  method  of  clamping  them  together  at  the  junction 
of  the  units,  while  the  latter  shows  their  use  in  the  construction  of  an 
all-concrete  dwelling.  In  general,  the  units  are  24"  square,  and  are 
made  of  No.  16  galvanized  sheet  iron,  reinforced  around  all  four  sides 
by  1"  x  1"  x  J/g"  steel  angles;  the  units  are  arranged  with  two  clamps  on 
the  right  hand  edge,  so  that  when  these  clamps  are  turned  into  posi- 
tion they  tie  the  adjacent  edges  of  the  units  together.  Besides  these 
clamps,  dowel-pins  are  provided  on  each  plate  which  fit  into  correspond- 
ing holes  in  the  adjoining  unit.     In  the  use  of  these  unit  forms  the  window 

I  106  ] 


Patent  steel  forms  used  in  concrete  wall  construction. 


Patented  steel  forms  in  use. 


107 


and  door  frames  are  set  in  conjunction  with  the  forms,  and  are  cast  in 
place.  In  order  to  make  the  construction  as  adjustable  as  possible  to 
any  dimensions,  other  widths  of  units  may  be  had  in  increments  of  two 
inches,  and  three-inch  plates  are  used  in  order  to  get  odd  sizes.  The  units 
are  tied  together  by  wire  ties  which  pass  through  holes  in  the  angles,  and  a 
detail  of  the  clamping  device  previously  described  is  shown  in  Fig.  72. 

Remarks  Regarding  Forms  and  Their  Construction. — It  is  an  ac- 
cepted fact  by  those  who  have  had  much  experience  in  concrete  con- 
struction that  it  is  not  economical  to  use  poor  grade  lumber  for  forms. 
The  cost  of  using  old  lumber,  because  of  the  work  required  to  patch  it, 
extract  the  nails,  and  prepare  it  so  as  to  give  results  in  any  way  satis- 
factory, is  greater  than  to  purchase  new. 

All  lumber  for  form  work  should  be  either  white  pine,  yellow  pine 
or  spruce;  hemlock  should  not  be  used  ordinarily  for  exposed  work. 
When  the  lumber  is  delivered  it  should  be  carefully  piled,  with  spaces  be- 
tween the  boards,  with  the  top  layer  pitched  to  shed  water,  and  where 
possible,  it  should  be  protected  from  the  sun.  It  is  vital  that  the  boards 
for  form  construction  shall  not  be  badly  warped  or  twisted,  and  any  care 
that  can  be  given  to  prevent  this  amply  repays  for  the  trouble. 

The  joints  in  form  construction  should  be  close — especially  where  a 
wet  mixture  of  concrete  is  used,  though  the  best  results  are  not  always 
obtained  by  using  matched  boards.  The  moisture  sometimes  causes  the 
wood  to  swell,  and  when  they  are  driven  up  tight  there  is  a  tendency  to 
buckle  which  sometimes  results  in  poor  work. 

It  is  of  the  utmost  importance  that  the  bottom  of  floor  forms  when 
in  place  shall  be  clean  of  all  shavings,  sawdust  and  chips  before  the  con- 
crete is  placed,  and  the  same  precaution  must  be  used  with  reference  to 
wall  forms. 

In  winter  time  all  form  work  must  of  course  be  clear  of  ice  or  snow 
before  the  concrete  is  placed.  In  summer  time,  or  hot  weather,  form 
work  should  be  kept  well  wetted  in  order  that  the  lumber  may  not  shrink 
and  leave  large  cracks  through  which  a  wet  mixture  of  concrete  will  run, 
and  by  which  unsightly  fins  or  markings  are  left  upon  the  concrete. 

[  108] 


£02 


:<* 


oQi 


fcj    Is 

£  o 

o 
u 

•3 

•a 


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o  E 


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It  is  not  well  in  house  construction  to  oil  the  forms.  In  the  first 
place,  it  is  apt  to  leave  the  concrete  discolored  and  stained  on  the  outside. 
It  is  also  likely  to  cause  trouble  where  the  concrete  is  plastered  on  the 
inside,  by  the  oil  coming  out  in  the  finished  plaster  work.  There  seems 
to  be  no  real  necessity  for  or  advantage  to  be  gained  in  oiling  either  wall 
or  floor  forms  in  the  construction  of  dwelling  houses. 

Selection  and  Care  of  Steel  Reinforcement. — It  is  generally  conceded 
that  any  type  of  deformed  steel  bar  is  superior  to  plain  round  rods  for 
the  purpose  of  reinforcing  concrete.  In  the  selection  of  the  type  of  de- 
formed bar  the  constructor  should  be  governed  by  the  pattern  of  bar  which 
is  most  available  in  the  locality  of  the  proposed  building  site.  If 
there  is  an  operation  contemplated,  which  would  require  a  great 
amount  of  steel  reinforcement,  then  prices  can  be  obtained  on  several 
types  of  deformed  bars,  with  the  idea  of  getting  the  best  possible  quota- 
tion. It  will  generally  be  found  that  the  most  available  deformed  rein- 
forcing bar  is  the  square  twisted  bar,  and  that  this  bar  fulfills  every  re- 
quirement of  a  uniform  net  section,  as  well  as  a  deformation  without  an 
increase  in  the  weight  of  the  bar. 

The  only  advantage  of  plain  round  bars  is  that  they  are  less  costly 
than  any  type  of  deformed  bar,  and  can  be  obtained  from  the  stock  of 
any  local  dealer  in  sufficient  quantity  for  the  construction  «{  a  concrete 
house  of  ordinary  dimensions. 

Where  reinforcing  steel  is  sent  from  the  mill,  or  even  from  a  distant 
wholesale  dealer  or  broker,  it  is  usually  shipped  in  open  freight  cars,  and 
generally  it  is  necessary  to  haul  the  steel  from  the  siding  or  freight  sta- 
tion. It  is  best,  if  possible,  to  haul  it  in  wagons  of  sufficient  length  to 
prevent  it  from  trailing  on  the  ground. 

In  any  construction  work  annoyance  and  loss  of  time  are  saved  by 
exercising  care  in  the  disposal  of  the  materials,  and  the  manner  of  taking 
care  of  steel  reinforcement  is  not  an  exception  to  this  rule.  The  steel, 
upon  delivery,  should  be  sorted  out  with  reference  to  the  position  it  oc- 
cupies in  the  building,  and  with  regard  to  sizes.  In  a  very  large  operation 
of  concrete  houses  the  steel  should  be  placed  in  racks  and  checked  off  as 

[in  ] 


used.  It  some  system  is  not  adopted  in  taking  care  of  the  steel  reinforc- 
ing bars,  it  will  be  found  that  some  of  the  longer  bars  will  be  used  in  places 
for  which  shorter  bars  were  ordered,  and  that  the  short  bars  left  over  will 
not  meet  the  requirements  of  the  conditions  for  which  the  longer  bars 
were  needed. 

All  steel  reinforcing  bars  before  being  placed  in  position  should  be 
cleaned  of  loose  scale  by  using  a  wire  brush.  They  should,  of  course, 
never  be  painted,  and  should  be  free  from  oil,  clay,  or  dirt.  Material  of 
this  kind  on  the  steel  will  destroy  its  bond  in  the  concrete. 

While  the  ordinary  steel  reinforcement  will  stand  a  great  amount 
of  rough  handling,  yet  it  is  best  not  to  attempt  to  bend  suddenly  or  other- 
wise subject  the  steel  to  severe  shocks,  especially  where  high  carbon  steel 
is  being  used,  as  sometimes  the  steel  rods  will  be  broken  off.  Accidents 
of  this  kind  are  more  likely  to  occur  in  cold  weather. 

Kinds  of  Steel  Used  for  Reinforcing. — Two  grades  of  steel  are  used 
in  the  manufacture  of  reinforcing  rods  or  bars,  generally  known  as  "high 
carbon"  and  "low  carbon '  steel.  Such  terms  are  probably  mislead- 
ing, as  usually  so-called  "high  carbon"  steel  is  made  by  the  Bessemer 
process,  and  has  an  ultimate  tensile  strength  of  between  80,000  and  90,- 
000  pounds,  while  the  steel  commonly  denominated  as  "low  carbon"  is 
made  by  the  open-hearth  process,  and  has  a  tensile  strength  of  from  60,000 
to  70,000  pounds.  There  is  also  what  is  known  as  "re-rolled "  steel,  which 
is  a  term  applied  to  reinforcing  bars  which  have  been  rolled  from  dis- 
carded railroad  rails,  these  being  split  up  and  the  heads  or  bulbs  of 
the  rails  being  rolled  into  reinforcing  bars.  The  re-rolled  material  is  gen- 
erally about  10  cents  per  cwt.  less  costly  than  the  newly  manufactured 
stock. 

Square  reinforcing  bars  are  frequently  designated  as  "cold-twisted" 
or  "hot-twisted,"  these  terms  being  applied  to  square  twisted  bars  which 
have  been  deformed  by  being  twisted  cold  or  hot  respectively. 

Selection  of  Kind  of  Steel. — There  is  considerable  diversity  of  opin- 
ion among  engineers  as  to  the  best  kind  of  steel  to  use  for  reinforcing 

[112] 


bars.  The  high  carbon  steel  gives  the  greater  tensile  resistance  and  also 
a  greater  elastic  limit,  but  it  is  also  less  ductile  and  can  be  bent  with  less 
surety  than  the  low  carbon  steel. 

In  concrete  dwellings  the  floor  loads  are  never  great,  and  the  labor 
is  less  likely  to  be  skilled  in  the  fabrication  of  the  steel,  so  that  it  would 
seem  best  to  use  steel  with  low  tensile  strength,  and  having  the  capability 
of  being  bent  cold  at  any  angle  without  sign  of  fracture  or  the  likelihood 
of  developing  flaws. 

Among  the  best  reinforcements  for  dwellings  are  woven-wire  fabrics. 
In  such  materials  the  wires  possess  great  tensile  strength  from  the  fact 
of  their  having  been  drawn  through  dies.  They  are  admirably  adapted 
to  concrete  construction  because  they  can  be  bought  in  rolls  of  any  length, 
and  being  a  fabric,  there  is  no  danger  of  misplacement  of  the  reinforce- 
ment. The  lighter  cross  wires  supply  without  any  care  or  attention  the 
necessary  shrinkage  rod. 

Price  and  Manner  in  which  Steel  Reinforcement  is  Sold. — All  steel 

rods  and  bars  are  sold  from  what  is  known  as  a  "base  price."  This  base 
price  is  for  all  rods  or  bars  of  %-inch  in  diameter  or  over.  If  the  bars 
are  less  in  size  than  %-inch  there  is  what  is  called  a  "size  differential," 
which  is  a  fractional  part  of  one  cent  a  pound  above  the  "base  price." 
The  present  differential  for  sizes  is  given  in  the  following  table: 


]  -inch  Bar. 


11 

1  6 


7 


5 

T?r 
i 

T 


Base. 

$  .05  per  cwt. 

•05 
.10 
.10 
.20 
•25 
•35 
•50 


This  schedule  of  size  differentials  is  based  on  plain  material.  Usually 
deformed  bars  cost  $2.00  or  more  a  ton  extra,  while  either  cold  or  hot 
twisting  adds  about  a  tenth  of  a  cent  a  pound,  or  $2.00  per  ton,  to  the 

8  [113] 


cost  of  plain  bars.  In  buying  reinforcing  steel  it  must  also  be  under- 
stood that  there  is  what  is  known  as  a  "shearing  differential,"  and 
also  a  "quantity  differential";  the  former  is  a  cost  of  .05  of  a  cent 
a  pound  on  all  bars  less  than  5  feet  in  length,  while  the  latter  is  a 
charge  of  .15  of  a  cent  a  pound  for  shipments  from  the  mill  of  less 
than  two  thousand  pounds. 

To  all  of  these  prices  must  be  added  the  freight  rate  from  the  mill 
to  the  point  of  delivery,  and  also  the  cost  of  hauling,  before  the  actual 

cost  per  pound  delivered  at 
the  site  can  be  determined. 

Use  of  Expanded  Metal 
and  Woven  Wire  Fabrics. — 

Both  expanded  metal  and 
woven  wire  fabrics  must  be 
handled  intelligently  in  the 
field. 

Expanded  metal  is  fur- 
nished in  gauges  from  4  to  18, 
in  sheets  6,  8,  and  12  feet  in 
length,  and  in  widths  of  from 
1  to  6  feet.  The  usual  way  of 
shipping  expanded  metal  is  in 
flat  bundles  containing  five  or 
six  sheets  wired  together. 

In  using  expanded  metal 
the  long  diagonal  of  the  mesh 
must  always  be  parallel  with  the  span  of  the  slab,  as  otherwise  the  full 
tensile  strength  of  the  material  is  not  obtained.  Expanded  metal  should 
be  lapped  on  the  ends  at  least  6  inches,  and  such  laps  should  occur  over 
points  of  support. 

In  using  wire  fabrics  it  is  well  to  interlace  them,  or  join  them,  at  the 
longitudinal  edges.  They  may  be  wired  together,  or  lock-woven  wire 
fabric  may  be  secured  along  the  edges,  as  illustrated  in  Fig.  74.     Some- 

[114] 


Fig.  74. — Attaching  the  edges  of  wire  reinforce- 
ment. 


times,  however,  merely  a  short  piece  of  wire  hooked  at  both  ends  is  used 
for  securing  the  edges  of  the  fabric. 

Methods  of  Bending,  Fabricating,  Securing  and  Placing  Reinforce- 
ment.— The  most  economical  practice  in  working  and  fabricating  steel 
reinforcement  is  to  make  careful  bills  of  material,  and  have  the  rein- 
forcing rods  or  bars  of  the  required  length  sent  to  the  site  of  the  operation, 
and  to  do  the  bending  and  fabricating  of  the  steel  on  the  operation. 


Fig.  75- — Hand  shear  for  cutting  reinforcement. 

There  is  always  some  cutting  to  do,  and  it  will  be  found  economical  to 
provide  on  the  job  a  hand-shear,  of  the  design  shown  in  Fig.  75.  With 
this  shear  rods  up  to  1  inch  square  can  be  cut  without  much  difficulty, 
especially  if  the  shear  is  securely  mounted  and  an  extension  is  made  to 
the  lever  by  means  of  a  piece  of  pipe.  Where  truss  or  other  rods  are  to 
be  bent,  diagrams  should  be  made  and  the  bars  bent  according  to  such 
diagrams. 

[115] 


There  are  a  number  of  simple  devices  that  can  be  arranged  to  facili- 
tate the  bending  of  rods  or  bars  to  the  required  angle.  One  of  the 
simplest  of  these  consists  of  a  strongly  constructed  table,  made  up  of  at 
least  8"  x  8"  pieces  securely  braced  and  fastened,  and  arranged  with  a 
cast  or  wrought  iron  plate  which  has  secured  to  it  an  iron  block  and  a 
movable  block  which  can  be  set  in  such  a  manner  as  to  clamp  the  steel, 
cither  by  means  of  wedges  or  by  clamping  devices,  as  illustrated  in  Fig.  76. 

Stirrups  may  be  bent  by  machine  and  sent  directly  from  the  shop, 
delivered  in  the  required  form,  or  else  they  may  be  bent  in  a  heavy  ma- 
chinist's vise,  such  a  vise  being  very  useful  when  securely  mounted,  for 
working  steel  reinforcement. 


Fig.  76. — Reinforcement  bending  table. 


It  is  very  seldom  in  house  construction  that  large-sized  reinforcing 
rods  would  be  used,  and  rods  up  to  1  inch  in  diameter  can  readily  be  bent 
cold.  Reinforcing  rods  larger  than  this  are  generally  heated  in  asmall 
portable  forge,  and  bent  while  hot. 

For  fastening  reinforcing  rods  and  bars  together,  and  for  securing 
the  stirrups,  as  well  as  for  fastening  cross-bars  in  wall  reinforcement,  and 
slab  rods,  no  better  method  has  been  found  than  that  of  wiring  them 
together.  This,  of  course,  can  be  done  with  pliers,  but  where  there  is 
much  to  do  the  device  illustrated  in  Fig.  76  has  been  used  success- 
fully, and  with  a  resultant  saving  in  time.     This  device  is  known  as 

[116] 


the  "Curry  Tyer,"  and  the  illustrations  show  clearly  the  method  of 
operating.  By  the  use  of  this  tool  the  wire  is  given  a  uniform  number  of 
twists,  and  the  rods  or  bars  are  secured  much  more  positively  than  can 
be  done  with  an  ordinary  plicr.  It  is  also  claimed  that  much  time  is 
saved  in  cold  weather  by  the  use  of  this  device,  as  with  ordinary  pliers 
the  work  is  necessarily  slow  from  the  fact  that  the  workmen's  hands 
become  numb. 

Protection  of  Work.— During  the  hardening  period,  concrete  should 
be  protected  from  sun,  wind,  and  frost.  In  house  construction  much  of 
this  protection  is  afforded  by  the  forms. 

Intense  heat  of  the  sun  in  midsummer  and  high,  dry  winds  tend  to 
evaporate  water  from  the  surface  of  green  concrete  and  thus  injure  its 
appearance.  This  is  easily  prevented  by  such  means  as  enclosing  and 
shading  the  concrete  with  canvas.  Freshly  placed  concrete,  even  though 
protected,  should  be  sprinkled  with  water  as  soon  as  this  can  be  done 
without  pitting  the  surface.  It  may  then  be  covered  with  sand,  if  expe- 
dient, and  thereafter  wet  as  often  as  necessary.  When  possible,  the  ex- 
posed surface  of  concrete  should  be  safeguarded  from  sun  and  wind  until 
the  concrete  has  attained  an  age  of  thirty-six  hours. 

Alternate  freezing  and  thawing  of  concrete  which  has  not  had  oppor- 
tunity to  set,  seriously  injure  it.  Consequently  it  has  been  customary, 
and  is  still  usual  practice,  to  conclude  all  concrete  work  in  early  winter 
as  soon  as  there  is  danger  of  freezing.  Within  recent  years,  methods  have 
been  adopted  by  means  of  which  urgent  concrete  work  is  done  even  in 
the  dead  of  winter.  Such  results  are  secured  either  by  lowering  the 
freezing-point  of  the  concrete  or  by  heating  the  materials  entering  into 
its  composition  and  by  protecting  the  concrete  after  it  has  been  placed. 

Ordinary  salt  is  the  cheapest  means  of  lowering  the  freezing-point  of 
concrete.  It  is  common  practice  to  dissolve  in  the  mixing  water  a  quan- 
tity of  salt  equivalent  to  one  per  cent,  (by  weight)  of  the  water  used  for 
each  degree  of  drop  in  temperature  below  the  freezing-point,  32°  Fahr. 
However,  not  more  than  ten  per  cent,  of  salt  should  be  used,  as  a  greater 
quantity  may  seriously  injure  the  concrete.     Consequently  this  preven- 

[«7l 


Fig.    77- — "Curry    Tyer. "      A    convenient    method    for    wiring    reinforcement 

together. 


[H8] 


( 


1  & 


J! 

S3 


(* 


tive  is  not  usable  for  temperatures  lower  than  22°  Fahr.  Calcium 
chloride  is  also  employed  for  the  same  purpose.  These  salts  should  not 
be  used  in  concrete  when  the  appearance  of  the  surface  is  a  matter  of 
consideration,  as  they  are  likely  to  show  in  spots  in  the  form  of  white 
efflorescence.  Also  in  reinforced  construction  there  is  probability  of  salt 
causing  the  steel  to  corrode. 

For  concreting  in  cold  weather  more  satisfactory  results  are  procured 
by  heating  the  aggregate  and  the  water  and  by  keeping  the  concrete 
warm  until  the  cement  has  set.  An  elaborate  and  expensive  plant  is  not 
necessary.  The  aggregate  may  be  heated  by  heaping  it  over  steam  pipes 
or  coils  or  by  piling  it  over  a  make-shift  furnace  consisting  of  an  old 
boiler,  a  metal  tube,  a  semi-circular  form,  or  other  simple  devices.  Like- 
wise water  for  mixing  may  be  heated  in  barrels  or  tanks  by  steam  coils 
or  pipes  or  in  tanks  by  a  furnace.  Frequently  it  is  drawn  directly  from  a 
boiler  used  to  generate  steam  for  other  purposes. 

Often,  even  when  the  temperature  of  the  air  is  above  the  freezing- 
point,  green  concrete  is  injured  by  the  use  of  frosty  aggregate.  Especi- 
ally in  early  spring  must  sand,  stone,  and  gravel  be  carefully  inspected 
to  see  that  they  contain  no  frost.  In  such  case  the  materials  must  be 
heated  as  in  freezing  weather.  Sometimes  a  stream  of  water  from  the 
well  or  hydrant  is  sufficiently  warm  to  dispel  the  frost  when  played  on  the 
aggregate. 

After  the  concrete  is  placed  in  the  forms,  it  is  sometimes  necessary 
to  prevent  it  from  freezing.  Often  the  forms  supply  adequate  protection 
for  all  except  exposed  surfaces,  which  should  be  covered  with  a  tarpaulin, 
boards,  or  building  paper,  freely  supported  a  couple  of  inches  above  the 
concrete.  Sand  and  clean  straw  are  also  used.  In  severe  weather  simi- 
lar additional  protection  is  given  the  concrete  in  the  forms  and  often  a  jet 
of  steam  is  introduced  under  the  tarpaulin  covering.  For  green  concrete 
floors  and  inside  work,  all  window  and  door  openings  are  tightly  closed  and 
the  interior  heated  by  salamanders,  sheet-iron  stoves,  or  furnaces. 

Concrete  amply  protected  in  freezing  weather  for  forty-eight  hours 
after  it  has  been  placed  is  out  of  danger  of  frost. 

Details  of  ornamentation  must  be  carefully  shielded  until  the  entire 

[121  1 


structure  is  completed.  Sharp  corners  can  be  protected  from  chipping  and 
spalling  by  placing  wooden  pieces  as  buffers  on  each  side.  Ornaments 
cast  as  independent  units  must  not  be  set  until  the  latest  time  permissible. 
Such  ornaments,  as  well  as  those  cast  in  place,  should  be  crated  and  en- 
closed with  canvas  to  protect  them  from  falling  debris  and  sticky  mortar. 

To  the  exterior  faces  of  tiles 
paper  is  glued  to  prevent  the 
chance  adhesion  of  cement  mor- 
tar and  is  later  removed  by  the 
application  of  water.  Concrete 
and  tile  ornaments  can  be 
cleaned  with  a  weak  solution  of 
acids,  as  described  under  "Sur- 
face Treatment"  on  page  129. 

Treatment  of  Concrete  Sur- 
faces.— As  in  the  design  of  a 
house,  the  treatment  of  a  con- 
crete surface  is  purely  a  matter 
of  individual  taste.  The  only 
thing  uponwhich  there  is  unanim- 
ity of  opinion  is  that  a  surface 
should  not  be  of  the  forbidding 
color  and  texture  sometimes 
found  in  sidewalks — a  surface 
perfectly  smooth  and  cold  and 
leaden  in  hue.  Some  architects 
have  designed  attractive  houses 
in  which  the  walls  were  left 
just  as  they  appeared  when  the  forms  were  removed.  Others  have 
adopted  this  plan  as  to  texture  of  surface,  following  with  a  wash  in  white 
or  color.  In  many  cases  walls  are  scrubbed  when  green,  resulting  in  the 
removal  of  the  cement  film  and  exposure  of  aggregates.  The  outer  coat- 
ing has  sometimes  been  removed  by  sand-blasting,  and  again  by  bush- 


Fig.  78. — Tamper  for  getting  mortar  face. 


hammering.  The  nature  of  concrete  is  such  that  it  affords  great  oppor- 
tunity for  the  architect  to  exercise  his  ingenuity  and  taste  in  producing 
satisfactory  results.  Various  methods  of  treating  surfaces  are  described 
below. 


Mortar  Facings  and  Untreated  Surfaces. — Where  utility  is  the  prin- 
cipal point  of  consideration,  a  surface  sufficiently  pleasing  for  the  purpose 
may  be  obtained  by  using  a  moderately  wet  mixture  (well  tamped)  and 
tightly   and    neatly  built   forms. 
With  such  a  concrete,  a  thin  film 
of  mortar  usually  settles  against 
thesidesof  the  forms.    Frequently, 
due  to  carelessness  and  the  bridg- 
ing   of    the    coarser    aggregates, 
small    pockets   appear   when  the 
forms    are    removed.      Such    an 
objectionable    feature    is     easily 
avoided,  either  by  spading  or  by 
the  use  of  facing  boards  (Figs.  78 
and  79). 

As  the  name  suggests,  spad- 
ing is  accomplished  by  means  of  a 
straight  garden  spade  or  a  special 
tool  of  similiar  shape,  which  is 
forced  down  and  worked  to  and  fro 
between  the  concrete  and  the  form 

in  order  to  force  back  the  coarser  aggregate  and  to  permit  the  flow  of  wet 
mortar  against  the  forms.  In  this  manner  a  surface  can  be  produced  which 
will  be  as  smooth  and  regular  as  that  of  the  forms.  Since  this  kind  of  sur- 
face treatment  requires  close  supervision  to  see  that  the  workmen  do  not 
neglect  to  use  the  spading  tool,  there  has  been  developed  a  more  depend- 
able method  which  secures  the  same  effect  by  means  of  a  device  called  a 
facing  board.  The  facing  board  consists  of  a  short  length,  usually  5 
feet,  of  yVinch  sheet-metal  plate,  10  to  12  inches  wide,  with  the  top  3 

[123] 


Fig-  79- — Facing  board. 


inches  bent  to  an  outward  flare.  To  the  inner  face  of  this  plate,  near  each 
end  and  at  the  middle,  are  riveted  short  vertical  lengths  of  one-inch  angle 
irons  and  simple  loop  lifting  handles.  In  operation  the  boards  are  set 
ends  abutting,  with  the  angle  spacers  against  the  inner  face  of  the  outside 
wall  form.  The  ordinary  concrete  is  placed  between  the  inside  wall  form 
and  the  facing  board,  while  the  one-inch  space  between  the  facing  board 
and  the  outer  form  is  filled  with  a  mushy  wet  mortar.  The  facing  board 
is  then  carefully  worked  up,  almost  out  of  the  concrete,  which  is 
again  tamped  lightly  so  as  to  insure  a  good  bond  between  the  ordinary 
concrete  and  the  facing  mortar.  This  operation  is  repeated  as  the  work 
progresses. 

By  using  the  original  method  of  a  dry  mix  and  tamping,  there  has 
come  into  use  a  surface  finish  which  in  boldness,  beauty,  and  execution 
of  detail  has  the  charming  appearance  of  free-hand  sketches.  Suitability 
of  design  and  careful  construction  of  forms  are  primary  requisites  of  this 
remarkable  treatment.  By  using  a  concrete  fairly  lean  in  Portland 
cement  and  somewhat  short  in  proportion  of  fine  aggregate,  and  by  tamp- 
ing the  concrete  thoroughly,  there  is  produced  a  surface  which  brings  out 
the  sharpness  of  detail  without  displaying  the  minor  irregularities  and 
imperfections  frequently  discernible  in  the  ordinary  mortar  finish. 
The  surface  obtained  has  all  the  charm,  warmth,  and  softness  of  a  coarse- 
grained stone.  Its  face  is  rough  and  deeply  pitted,  consequently  such 
work  is  often  mistaken  for  weathered  stone.  Exposure  to  the  elements 
for  several  years  has  brought  forth  no  evidence  of  injury  from  frost  and 
no  efflorescent  discoloration  of  surfaces  so  treated  (Fig.  80). 

For  such  untreated  surfaces  the  concrete  is  usually  proportioned  1 
part  cement  to  ij^  parts  sand  to  4^  parts  crushed  limestone  screenings, 
which  must  pass  a  3^-inch  mesh  and  be  retained  on  a  34-inch  screen. 
Such  a  small  amount  of  water  is  used  that,  when  the  concrete  is  tamped 
into  place,  no  mortar  flushes  to  the  surface. 

Abrased  and  Tooled  Surfaces. — Plain  mortar-facing  finishes,  al- 
though productive  of  a  smooth  surface,  are  not  always  satisfactory  for 
every  design.     To  erase  form  marks  and  to  produce  uniform  color,  tex- 

[124] 


ture  and  appearance,  such  surfaces  are  frequently  abrased  or  tooled. 
Three  forms  of  abrasion  are  in  good  practice — brushing,  scrubbing,  and 
sand-blasting. 

Brushing. — Simple  character  is  given  an  ordinary  mortar-faced  sur- 
face by  brushing  the  green  concrete  with  a  stiff  fiber  or  wire  brush. 
Special  brushes  of  slitted  sheet  metal  may  be  purchased  on  the  market  or 
can  be  made  by  clamping  together  strips  of  wire  cloth  or  ordinary  fly 
screen.     For  a  plain  brush  finish  it  is  advisable  that  the  facing  mortar  be 


Fig.  80. — Concrete  surface  that  corresponds  to  coarse-grained  building  stone. 

free  of  coarse  aggregate.  The  concrete  should  be  brushed  while  it  is  still 
green,  but  not  so  soon  as  to  remove  granular  particles  and  to  give  the 
surface  a  pitted  appearance.  The  length  of  time  between  the  placing  of 
the  concrete  and  the  removal  of  the  forms  for  this  finish  is  dependant 
upon  weather  conditions  and  the  amount  of  concrete  placed.  In  summer 
the  forms  should  usually  be  taken  down  on  the  day  following  the  placing: 
in  cooler  weather  greater  time  must  be  allowed.     The  older  the  concrete, 

!  125  1 


the  more  the  labor  required  to  produce  the  desired  effect.  Often  the 
forms  must  be  planned  and  built  in  sections  so  as  to  permit  early  removal 
and  to  facilitate  this  attractive  treatment.     (See  Fig.  81.) 

Scrubbing. — Where  the  forms  can  not  be  removed  quickly  enough  to 
permit  of  brushing,  similar  effects  are  obtained  by  scrubbing  the  concrete. 
Scrubbing  is  done  by  means  of  a  concrete  brick,  soft  limestone,  or  a  car- 
borundum stone.  As  soon  as  the  forms  can  be  removed,  the  concrete 
is  flushed  with  water  and  rubbed  vigorously  with  a  number  16  stone. 
After  the  roughness  and  the  cement  skin  have  been  removed,  the  lathered 
surface  is  washed  down,  dusted  with  the  i  .2  dry  mixture  of  cement  and 
sand,  and  the  scrubbing  is  completed  with  a  number  30  stone.  When  the 
desired  effect  is  obtained,  the  surplus  cement  grout  is  carefully  washed 
from  the  concrete  face.  This  treatment  produces  a  surface  lighter  in  ap- 
pearance than  that  of  ordinary  troweling,  and,  by  filling  the  pores  with 
cement  grouting,  yields  a  surface  at  least  as  entirely  waterproof  as  the 
original.  In  case  it  is  desired  to  treat  concrete  of  considerable  age,  there 
may  be  required  the  acid  treatment  described  under  "Exposed  Selected 
Aggregates,"  page  129.     (See  Fig.  82.) 

Sand-Blasting. — By  means  of  an  air  compressor,  a  small  gasoline 
engine,  and  a  hose  with  a  nozzle,  sand  can  be  so  forcibly  driven  against 
concrete  surface  as  to  remove  the  cement  film.  Several  days  previous 
to  such  treatment  all  imperfections  of  surface  should  be  touched  up  with 
mortar  or  removed  by  tooling  as  may  be  required.  Otherwise  in  at- 
tempting to  get  rid  of  these  irregularities,  the  surface  will  be  little  im- 
proved in  appearance.  If  it  is  desired  to  preserve  sharp  lines  of  archi- 
tectural detail,  these  should  be  protected  by  covering  with  heavy  paper  or 
wooden  strips.  Like  means  should  be  used  in  preventing  over-treatment 
and  in  obtaining  homogeneous  appearance  and  invisible  boundary  lines 
where  two  separately  applied  treatments  on  adjoining  sections  merge. 
For  blasting  purposes  a  clean,  sharp,  hard  silica  sand  or  crushed  quartz 
is  most  effective.  The  size  and  shape  of  the  nozzle  are  dependent  upon 
the  power  in  the  compressor,  the  range,  and  the  size  of  the  blasting  aggre- 
gate. For  materials  passing  a  number  8  and  a  number  12  screen,  a  \i 
inch  and  a  ^  inch  nozzle  are  respectively  used.     Likewise  correct  nozzle 

[  126  1 


Fig.  81. 


Fig.  82. 


fc, 


pressure  is  also  a  variable  quantity.  Usually  for  concrete  thirty  days 
old,  a  working  pressure  of  60  pounds  is  adequate.  Older  concrete  may 
require  as  much  as  80  pounds  pressure.  The  surface  resulting  from  such 
treatment  also  has  the  imprint  of  age  and  is  very  similiar  to  that  pro- 
duced by  scrubbing.  For  work  of  considerable  size  this  process  is  very 
rapid  and  inexpensive.     (See  Fig.  83.) 

Tooling. — The  lack  of  character  in  the  ordinary  mortar  finish  may 
be  got  rid  of  by  picking  the  surface  with  pointed  tools.  Such  treatment 
chips  off  the  mortar  on  the  outside  of  the  structure,  and  by  roughening 
the  surface  changes  it  from  a  monotonous  plane  to  a  wall  of  lively  and 
pleasing  texture.  Ordinary  hand-picks  and  stone-axes  have  been  used 
to  a  considerable  extent,  but  the  most  satisfactory  results  have  been  ob- 
tained by  means  of  the  hand  and  air-operated  bush-hammer. 

When  the  surface  is  to  be  bush-hammered,  the  concrete,  during  con- 
struction, should  be  faced  with  materials  suitable  for  rendering  the 
finished  results  desired.  Sand  mortars,  when  bush-hammered,  yield  a 
surface  of  very  uniform  appearance.  Where  the  surface  contains  coarse 
aggregate,  a  greater  variety  in  appearance  is  obtained.  Tn  order  to  pre- 
vent scaling  of  mortar  and  dislodging  of  coarse  aggregate,  the  concrete 
should  attain  considerable  age  before  being  treated.  Usually  such  treat- 
ment is  applied  when  the  structure  is  one  or  two  months  old.  In  three 
months  the  cement  generally  becomes  as  hard  as  the  aggregate,  and  such 
a  surface,  while  requiring  more  labor,  yields  greater  individuality. 

The  size  and  pointing  of  tools  for  hammering  are  matters  of  personal 
opinion.  Excellent  work  has  been  done  with  a  9-pound  hammer  with  32 
points  on  one  end  and  25  on  the  other,  and  also  with  a  hammer  of  the 
same  weight  with  16  and  25  points.  The  points  are  merely  small  pyra- 
mids spaced  about  two-thirds  of  an  inch.  On  large  construction,  pneu- 
matic tools  facilitate  the  work  and  cheapen  the  cost.  Variation  in  ap- 
pearance of  the  surface  may  be  effected  by  the  manner  in  which  the  stroke 
is  made.  Perpendicular  blows  merely  roughen,  while  glancing  strokes 
produce  lineal  markings.  Tooling  is  a  simple  and  effective  means  of 
dispelling  the  coldness  of  plain  concrete  surfaces.     (See  Fig.  84.) 

Displayed  Selected  Aggregates. — For  decorative  effect  and  variety  in 
9  I  129  ] 


color  and  composition  no  treatment  offers  the  architect  a  wider  field 
than  that  of  exposed  selected  aggregates.  A  wealth  of  color  is  everywhere 
at  hand  in  the  various  marbles,  burnt  clays,  gravels  and  granites,  from 
which  he  may  make  his  selection  of  crushed  aggregates  (one  or  several) 
and  combine  them  on  the  mixing  board  in  much  the  same  manner  as  the 
artist  mixes  his  paints.  Placed  in  the  wall  and  treated  so  as  to  display 
the  beauty  of  the  composition,  very  attractive  and  pleasing  results  are 


Fig.  84. 


obtained.  On  account  of  the  great  range  of  possibility  in  this  field 
definite  instruction  cannot  be  given  as  to  the  selection,  size,  grading  and 
proportioning  of  the  various  aggregates.  Such  details  depend  on  the 
subject  and  the  treatment  proposed.  After  these  factors  have  been  de- 
termined upon,  the  matter  reduces  itself  to  the  ordinary  problem  of  con- 
crete construction.  If  two  or  more  coarse  aggregates  are  used  they 
should  be  thoroughly  blended  before  being  mixed  with  the  sand  and 

[  130  ] 


A  window  in  the  residence  of  Albert  Mover.  South  Orange,  N.  J.  Tracy  &•  Swarlout.  Architects,  N. 

F«g-  85.— Wall  showing  beauty  of  displayed  selected  aggregates.  Also  a 
striking  example  of  the  harmony  of  concrete  and  tiles  or  mosaics  in 
rather  bold  relief. 


in  3= 

.5"° 

bo  a 


-J    -n 


cement  to  form  a  wet  concrete.  For  such  treatment  a  rich  mixture,  such 
as  a  1:2:4  or  a  1:23^:5  mix,  is  usually  desirable.  If  it  is  advisable  to 
economize  in  the  matter  of  selected  aggregates,  this  may  be  accom- 
plished by  the  use  of  facing  boards  (sec  page  123)  and  by  backing  up 
the  outside  layer  of  selected  aggregates  with  concrete  made  of  ordinary 
materials. 

Several  methods  are  practised  for  removing  the  cement  film  and  for 
displaying  the  color  of  the  concrete.  The  forms  may  be  taken  down  while 
the  concrete  is  yet  green  and  the  face  scrubbed  or  brushed.  Likewise  at 
the  proper  age  the  surface  may  be  tooled.  After  the  film  of  cement  has 
been  removed  to  brighten  up  the  colors  of  the  aggregate,  the  walls  should 
be  treated  to  one  or  more  applications  of  a  wash  composed  of  1  part 
commercial  hydrochloric  (muriatic)  acid  mixed  with  5  to  10  parts  of  clear 
water,  with  an  interval  of  several  minutes  between  the  applications. 
When  the  desired  effects  have  been  obtained,  usually  within  half  an  hour, 
the  walls  are  scrubbed  down  with  a  fiber  brush  and  are  afterward  flushed 
with  water  to  remove  the  acid  thoroughly.  Such  treatment  yields  a 
surface  rough  in  appearance  and  pleasing  in  color.     (See  Fig.  85.) 

If  a  smooth  surface  is  preferable  to  the  rough  appearance,  a  terrazzo 
effect  may  be  obtained  by  dressing  the  surface  with  a  carborundum  stone, 
as  described  under  "Abrased  and  Tooled  Surfaces."  By  such  means 
not  only  the  outside  cement  film  is  removed,  but  the  aggregates  are  also 
ground  down  smooth  and  given  a  polish.  Light,  portable,  power  grinding 
machines  are  now  on  the  market  which  quickly  and  economically  accom- 
plish this  work.  The  grinding  and  polishing  bring  out  the  beauty  of  each 
particle  of  aggregate  and  enhance  the  effect  by  leaving  it  in  a  setting  of 
cement. 

Colored  Surfaces. — For  decorative  effect  it  is  often  desirable  to  pro- 
duce a  concrete  of  a  shade  which  will  harmonize  with  some  general  color 
scheme.  This  may  be  accomplished  either  by  the  use  of  mineral  coloring 
matter  or  by  selected  aggregates  of  such  a  color  that,  when  made  into 
concrete,  the  desired  results  will  be  produced. 

Artificial  Colors. — The  use  of  artificial  colors  in  concrete  is  a  matter 
which  should  be  entered  into  only  after  careful  and  thorough  experimen- 

[133] 


tation  or  upon  advice  of  persons  familiar  with  all  factors  in  the  case. 
Only  mineral  pigment  should  be  used.  For  various  reasons  it  is  best  to 
use  a  color  facing-mortar  only  and  to  apply  it  by  means  of  facing  boards. 
Mix  the  colors  dry  with  the  cement,  and  in  making  concrete  use  this  mix- 
ture in  the  usual  way.  Sometimes  the  coloring  matter  is  added  to  the 
water.  To  produce  even  effects,  it  is  essential  to  measure  exactly  and 
carefully  mix  every  ingredient,  including  the  water.  Likewise  it  should 
be  remembered  that  mortar  when  wet  appears  several  shades  darker 
than  when  it  is  dried  out.  By  mixing  5  pounds  of  coloring  matter  with 
each  bag  of  cement  in  an  ordinary  1 .2  sand  mortar,  the  following  colors 
will  be  approximately  secured :  brown — roasted  iron  oxide ;  buff  to  yellow 
— yellow  ochre;  blue — ultramarine;  gray  to  dark  slate — lampblack  or 
carbon  black;  black — manganese  oxide,  eleven  pounds  per  bag.  By  in- 
creasing or  decreasing  the  proportion  of  coloring  matter,  various  hues 
may  be  obtained. 

Natural  Colors. — Through  the  use  of  many  natural  materials,  such 
as  marbles,  granites,  sandstones,  gravels,  burnt  clays,  corals  and  sands, 
results  far  preferable  to  artificial  colors  can  be  obtained.  These  materials 
are  crushed  fine  and  are  made  into  concrete  in  the  customary  manner. 
The  surface  coloring  is  brought  out  by  exactly  the  same  method  used  for 
displayed  selected  aggregates.  For  example,  beautiful  pinks  may  be 
obtained  with  red  marble  dust ;  a  terrazzo  effect  may  be  obtained  by  in- 
corporating with  the  red  marble  dust  a  few  black  and  white  marble  chips; 
or  a  slightly  different  effect  secured  by  using  black  and  white  marble 
screenings  alone.  Crushed  granite  or  feldspar  will  give  glitter  to  a  surface, 
and  so  on  an  infinite  number  of  effects  may  be  produced. 

Mosaic  Decoration. — One  of  the  most  popular  effects  is  obtained  by 
ornamenting  a  concrete  surface  with  colored  tiles.  In  working  out  orna- 
mentation two  general  methods  of  treatment  are  possible:  the  simple 
Roman  plan  of  using  tesserae,  in  which  the  design  is  formed  from  square 
or  nearly  square  pieces,  or  the  more  modern  way  of  cutting  the  clay  into 
units  of  sundry  shapes  to  conform  to  the  potter's  process  and  to  delineate 
the  design.     This  latter  method  is  comparable  to  that  used  in  stained- 

!i34) 


K5      c 


U 


be 


glass  windows.     The  cement  joints  correspond  to  the  lead  in  the  stained 
glass.     Either  plan  is  practicable. 

Several  methods  of  setting  tiles  are  in  use.  In  general,  careful  at- 
tention must  be  given  to  the  correct  lay-out  of  the  design  and  to  a  means 
of  fixing  it  securely  until  held  permanently  by  the  concrete.  In  walks 
and  floors  this  is  simply  a  matter  of  exact  location.  For  walls  and  ceilings 
the  entire  figure  is  often  molded  complete  or  in  sections  in  a  concrete  slab 
of  the  same  texture  as  that  of  the  wall  proper  and  later  set  in  place.  With 
this  and  similiar  schemes,  a  piece  of  heavy  paper  or  felt  is  placed  between 
the  form  and  the  face  of  the  tiles  to  prevent  them  from  being  stained  by 
liquid  cement.  Special  adhesive  substances  can  be  bought  or  made  by 
means  of  which  the  tiling  can  be  glued  in  exact  location  on  the  forms  and 
securely  held  there  until  backed  up  and  fixed  by  the  concrete.  (See  Fig. 
86.)  Later  the  application  of  water  dissolves  the  glue  and  leaves  the 
decorations  permanently  in  place.  Likewise  space  may  be  left  for  insert- 
ing the  decorations  later  by  lightly  nailing  to  the  inside  of  the  form  blocks 
of  wood  cut  to  the  shape  of  the  units  composing  the  design.  When  the 
forms  are  removed,  the  concrete  retains  the  wooden  block,  which  should 
be  left  in  position  until  the  concrete  surface  has  been  given  the  desired 
finish.  The  block  can  then  be  removed  and  the  ornament  set  in  place 
with  good  cement  mortar. 


136] 


Chapter  V 

Calculations  for  Determining  the  Strength  and  Design  of 
Reinforced  Concrete  in  House  Construction 


b]     J 


cq     S. 


Chapter  V 

Calculations  for  Determining  the  Strength  and  Design  of 
Reinforced  Concrete  in  House  Construction 

Principles  of  Reinforced  Concrete. — Concrete,  which  usually  consists  of 
broken  stone  embedded  in  or  cemented  together  with  a  mortar  con- 
sisting of  Portland  cement  mixed  with  gravel  or  sand,  partakes  of  the 
nature  of  an  artificial  stone,  and  becomes  monolithic  upon  the  harden- 
ing of  the  cement.  The  broken  stone  is  used  as  a  filling  material  to 
save  the  cost  of  the  more  expensive  cement,  and  is  known  as  the 
"aggregate,"  while  the  cementing  material  is  usually  designated  as  the 
"matrix." 

Concrete  has  great  compressive  resistance,  but  is  deficient  in  tensile 
strength.  The  great  discrepancy  between  the  compressive  resistance 
and  tensile  strength  of  concrete  is  as  the  ratio  of  I  to  10 — that  is,  plain 
concrete  of  the  usual  mixture  used  in  construction  work  has  for  its 
compressive  strength  10  times  its  strength  under  tension.  When  sub- 
jected to  tensile  stresses  it  is  still  further  weakened  and  made  unreliable 
by  the  possibility  of  cracks  or  flaws  occurring  on  account  of  the  shrinkage 
of  the  material.  These  defects,  which  sometimes  are  due  to  the  pouring 
and  setting  of  the  concrete,  would  not  decrease  the  compressive  strength, 
from  the  fact  that  should  such  cracks  or  flaws  occur  they  would,  under 
a  direct  compressive  stress,  be  brought  together,  and  the  two  blocks  would 
have,  in  spite  of  the  defect,  a  perfect  bearing  one  upon  the  other. 

The  Purpose  of  Steel  Reinforcement  in  Concrete. — Any  beam 
which  is  supported  at  its  ends,  and  sustains  weight  either  uniformly  dis- 
tributed or  concentrated,  is  subjected  to  bending,  and  transverse  stresses 

[  i39  1 


are  created.  The  transverse  stresses  in  a  beam  consist  of  compressive 
stresses  and  tensile  stresses.  In  the  upper  portion  of  the  section  of  a 
simple  beam,  as  shown  in  Fig.  87,  the  fibers  are  in  compression,  while  in 
the  lower  portion  the  material  is  subjected  to  tension.  An  imaginary 
plane  separating  these  two  directly  opposite  kinds  of  stresses  is  always 
denominated  the  "neutral  axis." 

Since  concrete  has  approximately  ten  times  as  much  compressive 
resistance  as  tensile  strength,  it  is  quite  evident  that  if  a  beam  was  made 
of  plain  concrete,  the  full  value  of  the  material  in  compression  could 
never  be  developed,  from  the  fact  that  it  has  such  a  low  value  in  tension 


Tension 


Fig.  87. — A  concrete  beam  without  reinforcement  and  stressed  beyond  elastic 
limit  would  fail  as  shown. 


in  that  portion  of  the  section  below  the  neutral  axis.  In  order  to  develop 
the  full  compressive  resistance  of  concrete  in  the  section  of  a  beam  above 
the  neutral  axis  steel  rods  or  bars  are  embedded  in  the  concrete  near  the 
lower  edge  or  soffit  of  the  beam.  Such  a  beam  is  said  to  be  "reinforced," 
and  is  economically  designed  when  sufficient  steel  is  embedded  in  the 
concrete  to  develop  the  full  compressive  resistance  of  the  concrete  in  the 
beam  section  above  the  neutral  axis. 

Steel  reinforcement  is  also  used  in  the  construction  of  columns  or 
posts  of  concrete  to  prevent  these  members  from  buckling  or  bending 
on  account  of  their  slender  proportions,  for  all  columns  over  10  diameters 
are  liable  to  transverse  stresses  corresponding  with  those  created  in  the 

[  140  ] 


beam.  These  stresses  are  developed  by  inequalities  in  the  strength  in 
the  section  or  by  eccentric  loading.  The  steel  reinforcing  rods  in  a 
column  also  prevent  the  column  from  shearing  along  an  oblique  line,  as 
the  type  of  failure  indicated  in  Fig.  88  is  quite  usual  when  reinforced 
concrete  columns  are  tested  to  failure. 


The  Use  of   Shrinkage  Rods  and  Bars. — Another  reason  for  using 
steel  embedded  in  concrete  is  for  the  purpose    of    tying  the  mass  of 
concrete  together  so  as  to  prevent  any  cracking  from  setting.     Many 
materials  are  subjected  to  a  reduction  in  size  in 
setting  or  hardening,  and  such  changes   in    the 
mass  are  apt,  where  other  parts  are  held,  to  pro- 
duce cracks.     By  binding  together  the  mass  of 
concrete,  whether  it  be  a  column  or  floor  slab, 
with  steel  rods  at  intervals,  such  shrinkage  cracks 
are  prevented. 

The  rods  or  bars  placed  in  the  concrete  for 
this  purpose  are  usually  designated  as  "shrinkage 
rods."  It  is  customary  to  introduce  shrinkage 
rods  in  floor  slabs  and  walls. 


■'!! 
•ii 

.      H. 

■ :  ■» 


offei/um 


Long/fod/na/ 

lxeinforTin<r  Rods 


Fig.  88. — Line  of  failure 
in  a  concrete  column 
when  stressed  beyond 
elastic  limit. 


Secondary  Reinforcement. — There  is  also  used 
in  both  columns  and  beams  what  is  designated 
as  "secondary  reinforcement. "  In  beams,  vertical 
or  oblique  stirrups,  as  illustrated  in  Fig.  89,  are 

usually  introduced.  These  stirrups  are  primarily  used  to  transmit  the 
stresses  from  the  main  reinforcing  rods  or  bars  to  the  concrete  in  the 
upper  section  of  the  beam.  They  also  prevent  the  beam  from  cracking 
along  oblique  lines,  as  illustrated  in  the  figure.  Such  cracks  are  called 
"diagonal  tension  cracks." 

It  will  be  noticed  from  the  illustration  that  these  stirrups  cross 
such  lines  of  defects,  and  prevent  them  by  giving  additional  tensile 
strength  at  right  angles  to  the  plane  of  these  faults.  In  columns,  the 
vertical  rods,  as  illustrated  in  Fig.  90,  are  tied  at  intervals  with  light 

I  141] 


iron,  looped  wires,  or  other  means,  in  much  the  same  manner  as  the  floor 
systems  tie  in  the  columns  of  a  building.     The  purpose  of  the  secondary 


5ide.  Ehy&t/on  of  End  of  Basm         Section 


Fig.  89. — Arrangement  of  reinforcement  in  beams. 

reinforcement  in  columns  is  to  prevent  the  long  longitudinal  rods  or  bars 
from  buckling  under  stress,  and  splitting  or  spalling  the  concrete  of  the 
column,  as  well  as  to  tie  together  the  mass  of  con- 
crete in  the  column. 


Arrangement  of  Primary  and  Secondary  Rein- 
forcement.— There  is  illustrated  in  Fig.  91  a  typical 
system  of  slab,  beam,  girder,  and  column  construction 
of  reinforced  concrete.  The  rods  or  bars  marked  "a" 
in  the  figure  are  the  main  reinforcing  rods,  and  it  will 
be  noticed  that  several  of  these  rods  or  bars  arc  bent 
up  at  the  ends,  and  extend  to  the  top  of  the  beam 
near  the  points  of  support.  This  is  done  in  order 
that  there  shall  be  additional  resistance  to  longitu- 
dinal shear,  and  also  to  prevent  the  diagonal  tension 
cracks  near  the  abutments.  Another  reason  for 
[  142  ] 


Fig.  go. — Position  of 
reinforcement  in 
columns. 


bending  some  of  the  rods  up  in  this  manner  is  to  provide  tensile  resist- 
ance at  the  top  of  the  beam  near  the  point  of  support,  so  as  to  resist 
what  is  called  the  "negative  moment." 

The  negative  moment,  or  contraflexture,  is  simply  the  changing  of 
the  stresses  to  opposite  kinds  where  the  ends  of  a  beam  are  fixed,  or  held 
rigidly.  When  these  bent-up  rods  lap  over  the  points  of  support  they 
tie  the  construction  together,  and  give  the  beam  the  advantage  of  con- 
tinuity. This  reduces  the  bending  moment  considerably,  although  it  is 
seldom  taken  into  account  in  the  design  of  concrete  beams  and  girders. 


Fig.  91. — Arrangement  of  primary  and  secondary  reinforcement. 


At  b  b  in  the  figure  is  shown  the  "secondary  reinforcement."  This 
secondary  reinforcement  consists  of  stirrups — usually  of  light  bar  iron, 
}/g"  x  1",  or  }/£"  or  Y%'  round,  bent  in  the  form  of  U-shaped  stirrups, 
which  interlace  with  the  main  reinforcing  bars  and  project  into  the  upper 
part  of  the  beam.  When  there  is  a  slab,  monolithic  with  the  beam, 
these  stirrups  are  carried  to  the  upper  part  of  the  slab.  The  number  of 
stirrups  required  and  the  proper  spacing  is  given  on  page  187. 

The  rods  or  bars  indicated  at  c  c  are  known  as  the  "slab  rods," 

[  i43  1 


and  extend  at  right  angles  to  the  beams,  thus  reinforcing  the  concrete 
slab.  These  bars  are  usually  from  }/£'  to  Y"  square  or  round,  being 
spaced  from  3"  to  8"  on  centers,  depending  upon  the  amount  of  resistance 
necessary  for  the  particular  spans  and  loads. 

It  is  usual  in  all  slab  reinforcement  to  provide  shrinkage  rods  or 
bars,  which  are  shown  in  the  illustration  at  d  d.  These  rods  are  generally 
very  light  bars,  about  }4"  square  or  round,  and  it  is  the  usual  practice 
to  place  them  about  24"  center  to  center. 

Besides  the  slab  reinforcement  and  shrinkage  bars,  it  is  considered 
good  practice  to  provide  what  is  known  as  "shear  bars"  over  all  main 
girders — "girders"  being  understood  as  the  concrete  supporting  members 
which  sustain  the  ends  of  the  beams.  These  shear  rods  are  intended  to 
increase  the  resistance  of  the  slab  over  the  top  of  the  girder,  and  are 
quite  frequently  made  of  the  same-sized  bars  as  the  slab  reinforcement. 
They  are  generally  5'  in  length,  and  spaced  12"  center  to  center. 

"Lap-rods"  or  "tie-bars"  are  placed  over  the  junction  of  all  beams 
and  girders  where  the  main  reinforcing  rods  do  not  lap.  Such  tie-rods 
are  made,  as  a  rule,  %"  square  or  round,  and  generally  about  5'  in  length. 
Sometimes  two  such  rods  are  placed  over  the  junction  of  girders,  and  one 
rod  over  the  junction  of  beams.  These  rods  are  indicated  in  the  illus- 
tration at  e. 

The  longitudinal  rods  in  columns  are  not,  as  a  rule,  decided  upon 
with  regard  to  their  number  and  area  by  any  fixed  formula.  The  general 
practice  is  to  put  in  enough  steel  to  equal  in  area  1  to  1  Y%  of  the  sec- 
tional area  of  the  concrete.  Longitudinal  column  rods  are  shown  in  the 
figure  at  /,  and  it  is  never  good  practice  to  make  these  rods  less  than  Y" 
in  diameter.  It  is  customary  to  extend  these  rods  above  the  floor  con- 
struction, so  that  the  rods  of  superimposed  columns  may  lap  with  them, 
the  lap  usually  being  made  about  2'  6"  in  length. 

The  longitudinal  rods  of  columns  are  always  tied  together  at  inter- 
vals with  either  )4"  round  ties,  or  else  held  in  position  with  wire  ties, 
or  ties  of  bar  iron  punched  so  as  to  allow  the  rods  to  pass  through.  The 
practice  is  to  make  these  ties  a  distance  apart  equal  to  the  diameter  of 
the  column,  never,  however,  exceeding  an  18"  pitch  or  spacing. 

[144] 


Strength  of  Concrete. — The  concrete  used  in  building  construc- 
tion is  usually  composed  of  a  1-2-4  mixture — that  is,  one  part 
Portland  cement,  two  parts  sand  or  fine  gravel,  and  four  parts  broken 
stone.  Sometimes  broken  slag  or  clean  boiler  cinders  are  substituted 
for  the  broken  stone,  in  which  case  the  concrete  is  known  as  "slag"  or 
"cinder"  concrete,  respectively.  It  is  poor  practice,  however,  to  use 
either  of  these  two  for  reinforced  concrete  for  building  construction, 
although  cinder  concrete  is  sometimes  used  for  floor  slabs  supported  on 
steel  beams. 

The  contractor  is  not  particularly  interested  in  the  ultimate  strength 
of  concrete,  but  he  is  interested  in  the  allowable  unit  working  stresses. 
These  allowable  unit  stresses  are  different  in  the  several  cities,  and  are 
fixed  by  the  building  laws.  Outside  of  the  jurisdiction  of  the  cities 
the  judgment  of  the  designer  is  the  governing  factor  in  deciding  upon 
these  values. 

In  all  instances  where  allowable  unit  stresses  are  given,  it  is  under- 
stood to  mean  the  stress  in  pounds  per  square  inch,  which  is  allowed  as 
a  basis  in  figuring  the  safe  working  strength  of  the  material!  The 
following  table  gives  the  allowable  compressive,  shear,  tensile  and  bond 
stresses  for  concrete  and  steel  used  by  the  best  conservative  practice  in 
the  design  of  reinforced  concrete  structures: 


TABLE   4— ALLOWABLE   WORKING   STRESSES   FOR   CONCRETE   WHEN 

REINFORCED 
(Stresses  are  in  Pounds  per  Square  Inch) 


Mixture 
1-2-4 

Compression 

under 

Transverse 

Stress 

Compression 
under 
Direct 
Stress 

Shearing 
Stress 

Bond  or 

A  dhesive 

Stress 

Stone  Concrete 

600 

500 

75 

50 

Slag  Concrete 

400 

300 

50 

40 

Cinder  Concrete 

250 

150 

25 

15 

The  most  important  values  in  the  table  are  the  direct  compressive 
values  of  reinforced  concrete,  used  in  figuring  the  strength  of  columns, 

[  i47  ] 


and  also  the  unit  compressive  strength  of  concrete  allowable  in  figuring 
the  strength  of  beams  and  girders.  The  values  of  shear  are  of  some  use 
in  figuring  the  shearing  resistance  of  beams  at  their  points  of  support. 
It  is  necessary  sometimes  to  determine  the  adhesive  strength  of  a  steel 
bar  or  rod  embedded  in  the  concrete,  and  here  the  bonding  stress  or  the 
grip  of  the  concrete  upon  the  steel  is  important. 

These  values  will  be  used  in  some  of  the  examples  in  design  given 
in  the  following  pages. 


Strength  of  Beams  and  Girders. — There  are  shown  in  Fig.  92 
at  (a)  and  (6),  diagrammatical  figures  which  show  the  distribution  of 
the  stresses  in  reinforced  concrete  beams,  based  on  usual  assumptions 

employed  by  engineers  in  deter- 


A 


■5+ributi'on  of  Stresses  m  Concrete 


.        Npuirril  A  cij 


Concrete  tak  es  no 


Fbsihon  of 


Steel. 


Stress  bek<coAx/s~ 


&J 


(b) 


Fig.  92. — Diagram   showing   distribution   of 
stresses  in  reinforced  concrete  beam. 


mining    their    strength.     These 
assumptions  are  as  follows : 

First:  That  the  steel  takes 
all  of  the  tensile  stress,  while  the 
concrete  takes  all  of  the  com- 
pressive stress. 

Second:    That  the  relative 
amounts  of    the    stresses    upon 
the  steel  and  concrete  are  in  direct  proportion  to  their  ratio  of  moduli 
of  elasticity. 

Third :  That  the  total  compressive  resistance  of  the  concrete  above 
the  neutral  axis  must  equal  the  total  tensile  resistance  of  the  steel. 

Fourth:  That  the  stresses  on  the  concrete  vary  directly  from  zero 
at  the  neutral  axis,  to  maximum  at  the  extreme  fiber;  thus  the  variation 
of  stress  in  the  section  above  the  neutral  axis  is  indicated  by  a  triangle. 

From  the  above  it  will  be  seen  that  reinforced  concrete  beams, 
being  a  composite  material,  differ  from  beam  sections  of  a  single  material, 
for  in  the  latter  the  neutral  axis  passes  through  the  center  of  gravity  of 
the  section,  whereas  in  reinforced  concrete  beams  the  neutral  axis  is 
constantly  shifted  by  changes  of  the  relative  percentage  of  the  steel  and 
concrete  in  the  section,  and  raises  or  lowers  in  order  to  adjust  the  direct 

[148] 


stresses  above  and  below  the  neutral  axis  to  comply  with  their  differences 
in  their  relative  stresses  and  strains.  The  one  important  thing,  there- 
fore, to  determine  before  the  strength  of  a  beam  section  can  be  ascer- 
tained, is  the  position  of  the  neutral  axis. 

Formula  for  Determining  the  Position  of  the  Neutral  Axis. — The 
location  of  the  neutral  axis  in  any  reinforced  concrete  beam  varies 
with  the  relative  percentage  of  steel,  with  the  quantity  of  the  con- 
crete, and  with  the  quality  of  the  concrete. 

The  formula  for  determining  the  position  of  the  neutral  axis  is 
applicable  to  both  rectangular  beams  and  beams  of  T-section.  This  is 
true  for  all  practical  purposes  because  in  beams  of  T-section  the  neutral  axis 
lies  so  close  to  the  bottom  of  the  slab  that  the  T-section  may  be  considered 
as  a  rectangular  beam  of  a  width  equal  to  the  available  extent  of  the  slab 
in  compression.     This  will  be  explained  in  conjunction  with  T-sections. 

The  formula  for  determining  the  distance  k,  or  the  percentage  of  the 
depth  which  the  neutral  axis  is  below  the  top  of  the  beam,  is  as  follows: 

k  =  v  (pn)2+2  pn  — pn 

The  values  in  this  formula  are  best  understood  by  referring  to  Fig. 
93  and  the  following  notation : 

k=  Ratio  of  the  depth  of  the  neutral  axis  from  the  top  of  the  beam 
to  the  effective  depth  d. 

p  =  Ratio  of  the  area  of  the  steel  to  the  area  of  the  concrete  in  the 
portion  of  the  beam  above  the  center  of  action  of  the  steel.  This 
is  true  because  the  2  or  3  inches  of  concrete  below  the  steel  is 
considered  merely  as  fireproofing. 

n=  Ratio  of  the  moduli  of  elasticity  of  the  steel  to  the  moduli  of 
elasticity  of  the  concrete.  In  the  best  practice  this  value  for 
stone  concrete  is  12,  and  the  values  for  slag  and  cinder  con- 
crete are,  respectively,  15  and  30,  though  sometimes  different 
values  for  these  are  used. 

The  formula  given  above  is  the  basic  formula  for  all  reinforced 
concrete  design,  and  as  illustrating  its  application  the  following  example 
is  interesting: 

[  149  1 


C0rr>pr*'  *>  &/&** 


Example:  At  what  percentage  of  the  distance  from  the  top  to  the 
center  of  action  of  the  steel  reinforcement  is  the  neutral 
axis  located,  providing  the  beam  is  of  rectangular  section 
and  is  reinforced  with  y6^  of  one  per  cent,  or  .006  of 
steel?  The  ratio  of  the  moduli  of  elasticity  of  the  two 
materials  is  1  to  12. 

Solution:  Referring  to  the  formula  k=V/(pn)2-f- 2  pn—pn  the  values 
of  p  and  n  are  respectively  .006  and  12;  then,  by  substi- 
tution the  value  of 

k=V(.oo6  X  i2)2+2  X  .006  X  12-.006  X  12 
or,  k=V.oo5i84+.i44—  .072  =.314.  Answer. 

It  is  customary  not  to  work  out  these   formulas  every  time  the 
distance  k  is  desired  for  any  particular  percentage  of  steel  reinforce- 
ment, but  to  refer  to  a  table  giving  these 
values.     Such  a  table  is  given   on  page 
I5i- 

Determination  of  the  Distance  Jd. — 

The  necessity  for  obtaining  the  distance 
from  the  top  of  a  reinforced  concrete 
beam  to  the  neutral  axis  is  to  locate 
the  center  of  gravity  of  the  compressive 
stresses  in  the  concrete  above  the  neutral 
axis. 

Referring  to  Fig.  93,  it  will  be  seen  that  the  stress  in  the  concrete 
varies  from  zero  at  the  neutral  axis  to  maximum  at  the  extreme  upper 
edge  of  the  beam.  As  this  variation  is  uniform  under  working  stresses, 
the  variation  in  the  compressive  stresses  can  be  represented  as  a  triangle. 
The  center  of  action  of  the  compressive  stresses  is,  therefore,  at  the 
center  of  gravity  of  this  triangle,  and  is  consequently  located  at  one- 
third  of  the  altitude  of  the  triangle  from  the  base,  or  is  equal  to  — , 
when  kd  is  the  distance  of  the  neutral  axis  from  the  top  of  the  beam,  and 
the  lever  arm  with  which  the  concrete  and  steel  reacts  can  be  designated 
as  jd,  and  can  be  determined  directly,  when  the  neutral  axis  has  been 
located.     The  value  j  varies,  of  course,  with  the  variation  in  the  value  of 

[150] 


Fig-  93- 


k.  The  value  of  k  is  determined  by  the  ratio  of  the  steel  reinforcement 
and  the  ratios  of  the  moduli  of  elasticity.  Consequently,  a  table  which 
gives  the  value  of  j,  referring  to  Fig.  93,  in  ratio  of  the  distance  d, 
is  valuable,  as  it  gives  the  lever  arm  which  determines  the  resisting 
moment  of  the  steel  reinforcing  rods  or  bars  used  in  the  beam. 

The  values  of  j  for  different  ratios  of  steel  reinforcement  and  for 
different  values  of  n,  or  the  ratios  of  the  moduli  of  elasticity  of  the 
steel  and  concrete,  are  given  in  the  following  table: 

TABLE  5 


Values 
ofp 


.001 
.002 
.003 
.004 
.005 
.006 
.007 
.008 
.009 
.010 
.012 
.014 
.016 
.018 
.020 
.030 
.040 
.050 


N  =  io 
Values  of  k  and  j 


N=I2 

Values  of  k  and  j 


N  =  i5 
Values  of  k  andj 


k  = 


132 


k  = 

181 

k  = 

217 

k  = 

246 

k  = 

270 

k  = 

292 

k  = 

3ii 

k  = 

328 

k  = 

344 

k  = 

35« 

k  = 

3H4 

k  = 

407 

k  = 

428 

k  = 

446 

k  = 

4<>3 

k  = 

531 

k  = 

580 

k  = 

618 

j  =  .940 
J=-927 
3=918 
j=.9io 

j  =  903 
j=.896 
j=.89i 
j=.885 
j=.88i 

j=.872 

j=.864 
J=.857 
j=-85i 
j=.844 
j=.823 
j  =  .8o7 
j  =794 


k  =  .i43 

=  .952 

k  = 

196 

=  •935 

k  = 

236 

=  .922 

k  = 

266 

=  .911 

k  = 

291 

=  .903 

k  = 

3H 

=  .896 

k  = 

334 

=  .889 

k  = 

352 

=  .883 

k  = 

37o 

=  .877 

k  = 

384 

=  .872 

k  = 

411 

=  .863 

k  = 

435 

=  •855 

k  = 

456 

=  .848 

k  = 

476 

=  .841 

k  = 

493 

=  .836 

k  = 

56i 

=  .813 

k  = 

610 

=  .796 

k  = 

650 

=  783 

k  =  .i58 
k  =  .2i5 
k  =  .258 
k  =  .29i 
k  =  .3i9 

k  =  -343 
k  =  .366 
k  =  .384 
k  =  .40i 
k  =  4i7 
k  =  444 
k  =  47o 
k  =  .492 
k  =  -5i3 
k  =  .53« 
k  =  .600 
k  =  .650 
k  =  .686 


=  •947 
=  .928 

=  •914 
=  .903 

=  •894 
=  .885 
=  .878 
=  .872 
=  .866 
=  .861 
=  .852 
=  .843 
=  .836 
=  .829 
=  .823 
=  .800 
=  .784 
J  =-771 


Resisting  Moment  of  Rectangular  Beams  (Considering  the  Steel). — 
In  order  to  determine  the  resisting  moment  of  a  reinforced  con- 
crete beam  it  is  only  necessary  to  find  what  percentage  the  area  of  the 
steel  bears  to  the  area  of  the  concrete  in  the  beam  section,  and  select 
from  the  above,  Table  5,  the  value  of  j.  The  product  of  the  value  j, 
the  distance  from  the  center  of  action  of  the  steel  to  the  top  of  the  beam 
(d),  and  the  total  safe  working  stress  of  the  steel  (a  s),  will  give  the  resist- 
ing moment  of  the  beam.     This  can  best  be  expressed  by  the  formula 

Mi=jdas 
[  151  1 


In  this  formula 


Mi  =  the  resisting  moment  of  the  beam  in  inch-pounds; 

d    =the  distance  from  the  center  of  action  of  steel  reinforcement 

to  the  top  of  the  beam; 
a    =  the  total  area  of  the  steel  reinforcing  rods,  and 
s     =the  safe  unit  tensile  stress  of  the  steel,  which  is  generally  taken 

at  16,000  pounds. 

In    determining    the   ratio  of  the   steel,   in   order    to  obtain    the 
corresponding  value  j  in  the  table,  the  area  of  the  concrete  is  always 

considered  as  the  width  of  the 
beam  multiplied  by  the  dis- 
tance from  the  top  of  the 
beam  to  the  center  of  action 
of  the  steel,  as  the  concrete 
below  the  reinforcing  rods  or 
bars  is  not  a  part  of  the  theo- 
retical beam,  and  acts  only  as 
fireproofing  for  the  steel  rein- 
forcing rods. 


&20' 


J*SS6 


Fig.  94. 


Solution : 


Example :  Determine  the  re- 
sisting moment 
of  the  rectangu- 
lar reinforced 
concrete  beam 
illustrated  in  Fig. 
94. 
The  total  area  of  the  concrete  from  the  center  of  action 
of  the  steel  to  the  top  edge  is  10"  x  20"  =  200  square 
inches.  As  the  reinforcing  rods  or  bars  are  %"  square, 
the  sectional  area  of  one  rod  is  .5625,  and  2  rods  or  bars 
will  have  a  sectional  area  of  1.125;  hence  the  ratio  of 
steel  reinforcement  in  the  section  of  the  beam  is 
1.125-^200  =.0056 

Assume  that  N  =  12. 

From  Table  5  it  will  be  seen  that  the  ratio  of  the  lever 

[152] 


Detail  of  residence  of  Mrs.  Gaston  Daus,  Ocean  City,  N.  J.  Grant  M.  Simon,  Architect,  Pkila. 

Porch  return  constructed  of  solid  concrete,  which  means  elimination  of 
cost  for  up-keep.     Note  untreated  surface  of  house  walls. 


ft, 

-.-  -a 

■5   "a 


Q   — 


*5     ,Ji 


Z.   2s 


arm,  or  j,  for  the  ratio  of  steel  reinforcement,  or  .006,  is 
.896,  so  that  in  inches  the  lever  arm  with  which  the  steel 
acts  about  the  center  of  compression  is 

20  X  .896  =  17.9  inches  =  jd. 

The  resisting  moment  of  the  reinforced  concrete  beam  can  be  found 
by  substitution  in  the  formula  Mi  =  j  d  a  s,  so  that 

Mi  =  I7.9  X  1. 125  X  16,000  =  322,200  inch-pounds. 

Resisting  Moment  of  a  Rectangular  Beam  Section,  Considering 
the  Concrete. — In  reinforced  concrete  beams  of  rectangular  section 
the  strength  of  the  two  materials  must  be  considered — that  is,  the 
resisting  moment  of  the  steel  reinforcement  must  be  found,  and  if  there 
is  any  doubt  about  the  concrete  in  compression  when  stressed  to  its 
maximum  working  stress  at  the  extreme  fiber,  then  its  resistance  must 
be  determined  as  well,  and  the  least  resisting  moment  considered  as  the 
one  limiting  the  strength  of  the  beam  section. 

In  all  reinforced  concrete  beams  when  the  percentage  of  steel  is 
such  that  the  concrete  and  steel  are  of  equal  resistance,  and  both  are 
fully  stressed  to  their  allowable  unit  working  stresses  when  the  beam 
section  is  developing  its  maximum  allowable  resistance,  the  beam  is 
said  to  be  reinforced  with  a  critical  percentage  of  steel.  This  critical 
percentage  of  steel  is  always  the  same  for  fixed  unit  stresses  and  moduli 
of  elasticity,  so  that  if  the  steel  reinforcement  is  below  the  critical  per- 
centage, the  strength  of  the  concrete  need  not  be  questioned,  and  the 
resistance  of  the  steel  alone  is  considered. 

The  resisting  moment  of  the  concrete  above  the  neutral  axis  may 
be  found  as  simply  in  a  rectangular  beam  as  the  resisting  moment  of  the 
steel  reinforcement,  when  once  the  neutral  axis  has  been  determined  for 
the  percentage  of  steel  used  as  reinforcement. 

In  a  rectangular  reinforced  concrete  beam  the  intensity  of  stress  at 
the  neutral  axis  is  zero,  while  at  the  extreme  fiber  it  may  be  as  high  as  the 
maximum  allowable  compressive  stress  for  concrete  in  compression  when 
subjected  to  transverse  stress.     The  average  is  therefore  one-half  of  the 

[155] 


maximum  stress,  so  that  if  the  maximum  unit  compressive  strength  of 
the  concrete  is  taken  at  600  pounds,  the  average  stress  will  be  600  -4-  2  =  300 
pounds  per  square  inch.  In  order  therefore  to  determine  the  resistance 
of  the  concrete  above  the  neutral  axis  all  that  is  necessary  to  do  is  to 
multiply  the  area  of  the  cross-section  of  the  beam  above  the  neutral  axis 
by  the  average  unit  compressive  resistance  of  the  concrete,  the  product, 
in  turn,  being  multiplied  by  the  distance  from  the  center  of  action  of  the 
steel  reinforcement  to  the  center  of  action  of  the  compressive  area  of  the 
concrete. 

As  previously  stated,  the  location  of  the  center  of  the  compressive 
area  is  one-third  of  the  distance  from  the  top  of  the  beam  to  the  neutral 

axis,  or      ,  and  the  lever  arm  with  which  the  concrete  acts  about  the 

.  3 
steel  reinforcement  is  j  d,  so  that  the  resisting  moment  of  the  beam 

section,  with  regard  to  the  compressive  resistance  of  the  concrete,  may 

be  found  by  the  following  formula: 

Mc  =  kj  d2bc 

2 

in  which 

Mc=the  resisting  moment  with  regard  to  the  compressive  re- 
sistance of  the  concrete. 

k  =  ratio  of  the  distance  from  the  top  of  the  beam  to  the 
neutral  axis  to  the  distance  d. 

j  =  ratio  of  the  distance  between  the  center  of  compression 
in  the  concrete  and  the  center  of  action  of  the  steel,  to  the 
distance  d. 

d  =the  distance  from  the  center  of  action  of  the  steel  to  the 
top  of  the  beam. 

b     =  the  width  of  the  beam. 

c  =the  maximum  unit  allowable  compressive  resistance  of 
the  concrete. 

Example:  Determine  the  resisting  moment  of  the  reinforced  con- 
crete beam  shown  in  Fig.  94,  considering  the  concrete. 

Solution:  As  found  in  the  previous  example,  the  ratio  j  =  .896; 
and  from  Fig.  94  =  d  =  2o";  b  also  is  determined  from 
the  figure  as  being  10";  while  k  =  .3i4,  as  also  deter- 
mined  from  Table  5.     In    this    instance  the   allowable 

[156] 


compressive  resistance  of  the  concrete  will  be   taken  as 
600  lbs.     Therefore,  by  substitution  in  the  formula 


Mc  = 


.314  X  .896  X  20  X  20  X  10  X  600 


337,612  inch-pounds. 


Beams  of  T-section. — Where  reinforced  concrete  beams  or  girders 
support  and  are  monolithic  with  a  concrete  floor  slab,  in  analyzing 
the  strength  of  the  beam  or  girder  it  is  considered  as  a  T-section.  The 
form  of  the  beam  section  thus  considered  is  shown  in  Fig.  95,  and  it  will 
be  seen  that  by  the  adoption  of  this  section  the  available  amount  of  the 
concrete  in  compression  is  greatly  increased  over  that  which  would  exist 
in  a  simple  rectangular  beam. 

In  the  analysis  of  a  beam  of  T-section  to  determine  its  strength  or 


/ncrea&e  /»  Cotn/?re6£>/ot7  becav&e  0/  7es-  £ec//o*7 


#••■*•* :*.■«.■••'■?*.-  i. ■-«  *■'■*■  ■■-■ 


A/eu/ra/  /Jx/2 


£/ee/  //r  7errs>/o/? 


Fig-  95- — Increased  area  over  which  compressive  stress  acts  when  beam  and 
slab  are  molded  as  a  monolith. 


resisting  moment,  it  is  a  question  as  to  what  width  of  slab  can  be  consid- 
ered as  acting  homogeneously  with  the  beam.  A  conservative  rule  is 
that  the  width  of  the  T-section  shall  not  be  over  20  times  the  thickness 
of  the  slab.  For  instance,  if  the  slab  is  4"  in  thickness,  the  width  of  the 
slab  incorporated  in  the  T-section  would  be  80  inches,  provided,  of  course, 
that  this  distance  does  not  extend  the  slab  past  the  middle  of  the  distance 
between  the  two  beams.  Where  the  beams  are  closer  together  than  20 
times  the  thickness  of  the  slab,  the  flange  of  the  T-section  is  considered 
to  extend  a  distance  on  each  side  of  the  beam  equal  to  one-half  the  dis- 
tance to  the  next  beam. 

In  the  recently  prepared  Building  Laws  of  the  city  of  New  York 

[157] 


the  width  of  the  slab  to  be  incorporated  with  the  beam  in  forming  the 
T-section  is  limited  to  one-sixth  the  span  of  the  beam,  but  is  not  to  be 
greater  than  six  times  the  thickness  of  the  slab  on  either  side  of  the  beam. 
The  important  factor  to  determine  in  the  analysis  of  a  beam  of 
T-section  is,  as  with  rectangular  beams,  the  location  of  the  neutral  axis; 
but  the  extreme  strength  of  a  reinforced  concrete  beam  of  T-section  can 
be  very  simply  found  by  making  an  assumption,  which  is  seldom  much 
in  error,  and  is  consequently  sufficiently  safe  for  practical  purposes, 
especially  when  it  is  realized  that  because  of  the  assumptions  made  in 
calculating  the  bending  moments,  reinforced  concrete  construction  has 

an   actual   factor  of   safety  far 
r- 80' — ■ "1       above  that  used. 


E- j 20  tinted  / j "t 


\*T*T 


Fig.  96. 


•  tw  A?/» 


Approximate  Determination 
of  the  Strength  of  the  T-Sec- 
tion. — To  determine  approxi- 
mately the  resisting  moment  of 
a  reinforced  concrete  beam  of 
T-section,  reference  is  made  to 
Fig.  96.  As  previously  stated, 
the  reinforced  concrete  beam,  being  composed  of  two  materials  of 
different  strength,  it  is  necessary  to  find  the  resistance  of  each  under 
the  stresses  due  to  the  load,  and  to  limit  the  load  on  the  beam  so  that 
the  allowable  strength  of  the  weaker  material  will  not  be  exceeded. 
Nearly  always  in  reinforced  concrete  beams  of  T-section — and  it  would 
be  especially  so  in  house  construction — there  is  ample  concrete  in  compres- 
sion, and  the  steel  is  the  limiting  factor.  Another  assumption  that  is 
to  be  made  in  determining  the  approximate  strength  of  T-sections  is 
the  location  of  the  center  of  action  of  compression  in  the  slab,  and  one 
which  is,  on  an  average,  nearly  always  safe  to  make,  is  to  assume  the 
center  of  action  to  be  at  the  center  of  the  slab.  When  this  assumption  is 
made,  the  resisting  moment  of  the  steel  may  be  expressed  by  the  follow- 
ing formula: 

Ms  =  as  D 
[158] 


In  this  formula 

Ms=the  resisting  moment  of  the  beam  section  in  inch-pounds, 
considering  the  steel. 

a     =  the  total  area  of  the  steel  reinforcement. 

s     =  the  safe  unit  fiber  stress  to  which  the  steel  is  to  be  subjected. 

D  =the  distance  from  the  center  of  action  of  the  steel  reinforce- 
ment to  the  center  of  the  slab. 

Example:  Assume  that  the  beam  section  shown  in  Fig.  96  is  rein- 
forced with  four  \"  square  twisted  bars,  and  that  a  safe 
unit  stress  on  the  steel  of  16,000  pounds  is  to  be  considered 
as  the  working  stress.  What  will  be  the  resisting  moment, 
and  what  load,  including  weight  of  beam  and  slab,  will  the 
beam  carry  providing  it  has  a  span  of  20  feet? 

Solution:    By  substitution  in  the  above  formula 

Ms  =  4  X  16,000  X  20  =  1,280,000  inch-pounds. 

If  this  is  the  resisting  moment  in  inch-pounds,  and  the 
bending  moment  of  any  simple  beam  uniformly  loaded  is 
equal  to  M  =  1  x/i  W  L,  where  W  is  the  total  load  per 
square  foot  and  L  is  the  span  in  feet,  the  total  load 
that  the  beam  will  support  can  readily  be  found  by  the 
formula 

Ms  1,280.000 

W=.|   orW=  ,i   v  _n  =42,666  pounds.     Answer. 

I  2*-'  I  J     /\   20 

To  Determine  Whether  there  is  Sufficient  Concrete  in  Compression, 
Approximately. — In  conservative  practice  in  the  design  of  reinforced 
concrete  work  it  is  usual  to  stress  the  extreme  fiber,  or  upper 
edge  of  the  section  in  compression  under  transverse  stress,  to  a 
working  stress  of  600  pounds.  It  is  also  understood  that  the  stress  in 
the  concrete  at  the  neutral  axis  is  zero.  In  determining  the  approximate 
resistance  of  a  T-section  considering  the  steel  reinforcement,  as  explained 
on  page  158,  the  position  of  the  center  of  action  of  the  concrete  in  com- 
pression was  assumed  as  at  the  center  of  the  slab.  This  assumption 
makes  the  neutral  axis  pass  through  the  web  of  the  beam  at  a  distance 
below  the  slab  equal  to  one-half  the  thickness  of  the  slab.  The  variation 
of  the  compressive  stresses  in  the  concrete  is  uniform  from  the  neutral 

[159] 


axis  to  the  extreme  upper  edge  of  the  slab,  so  that  the  safe  allowable 
unit  stress  at  the  bottom  of  the  slab  would  be  one-third  of  the  maximum 
allowable,  or  200  pounds,  and  the  average  allowable  stress  in  the  slab 
section  would  be  equal  to 

600+200 
— ,  or  400  pounds. 

One  of  the  first  principles  of  engineering  is  that,  for  every  force 
acting  in  one  direction  in  a  body  in  equilibrium  there  must  be  a  corre- 
sponding and  equal  force  acting  in  the  opposite  direction;  therefore  the 
total  resistance  of  the  concrete  must  at  least  be  equal  to  the  total  resis- 
tance of  the  steel.  To  determine,  then,  approximately,  whether  the 
beam  has  sufficient  concrete  in  compression  in  a  slab,  all  that  is  necessary 
to  do  is  to  compare  the  strength  of  the  steel  reinforcement  with  the 
direct  resistance  of  the  portion  of  the  concrete  considered  as  being  in 
compression,  or  more  directly,  the  average  stress  in  the  concrete  must 
not  exceed  400,  so  that  the  results  obtained  by  the  following  formula 
must  be  within  this  limit:  c  =  7—; 
in  which  b  =  the  width  of  the  slab  in  compression ; 
t  =the  thickness. 

Example:  Determine  whether  the  concrete  in  the  slab  section  shown 
in  Fig.  96  is  sufficient  to  give  the  full  resistance  of  the 
steel  at  16,000  pounds. 

Solution:  The  total  area  of  the  steel  is  4  square  inches,  and  the 
fiber  stress,  or  safe  unit  tensile  resistance,  is  16,000  pounds. 
As  the  slab  is  4  inches  in  thickness,  the  available  width 
of  slab  is  4  X  20,  or  80  inches.  These  values  having  been 
obtained,  substitution  can  be  made  in  the  above  formula 
as  follows: 

_     4  X  16,000 

C  =  ~ g7T~v  a~  =  20°  Poun"s ' 

showing  that  the  concrete  is  only  stressed  up  to  one-half 
of  its  allowable  compressive  resistance  and  is  perfectly 
safe. 

[  160] 


h    ~ 


2     C 

c    a 


t    « 


"0 

c 
o 


M 


Example  of  the  adaptability  and  economy  of  concrete  in  stairway  con- 
struction. 


More  Accurate  Method  of  Determining  the  Resisting  Moment  of  T- 
sections  (Considering  the  Steel). — In  order  to  accurately  determine 
the  resisting  moment  of  reinforced  concrete  beams  of  T-section,  the  loca- 
tion of  the  neutral  axis  x  x,  Fig.  96,  must  be  determined. 

It  is  a  generally  accepted  practice  in  locating  the  neutral  axis  for 
beams  of  T-section,  to  consider  that  the  beam  is  a  rectangular  beam,  as 
included  within  the  lines  a,  b,  c,  d.  There  is  very  little  chance  of  error  in 
this  assumption,  for  the  reason  that  the  neutral  axis  quite  frequently  falls 
within  the  slab,  and  even  though  it  should  fall  below  the  bottom  of  the 
slab,  the  small  section  of  the  concrete  represented  by  the  shaded  areas  can 
be  practically  included.  The  chance  of  error  is  particularly  reduced 
because  the  portion  of  the  concrete  below  the  neutral  axis  is  never  taken 
into  account  in  determining  the  strength  factors  of  the  section. 

In  finding  the  location  of  the  neutral  axis  xx,  or  the  distance  kd,  the 
same  formula  as  that  applied  for  the  determination  of  the  same  distance 
in  rectangular  beams  is  used,  namely: 

k  =  v(p  n)2+2  p  n  — p  n. 

Before  applying  this  formula  it  will  be  necessary  to  determine  upon 
the  values  p  and  n.  If  the  T-section  illustrated  in  Fig.  97  is  taken  as  an 
example,  the   value   p   is   equal   to  ^— - —  =  .00454;    the  value   of   n  is 

oO  /\  22 

ordinarily  taken,  for  stone  concrete,  at  12,  so  that  by  substitution  in  the 
formula 

k  =  V\.oo454  X  X2V-  +  2  X  .00454  X  12 —  .00454  X  i2  =  .28oi 

As  the  distance  d,  Fig.  96,  is  22  inches,  the  actual  distance  from  the  top 
of  the  slab  to  the  neutral  axis,  or  the  line  x  x,  is 

.2801  X  22  =  5.16  inches, 

showing  that  the  neutral  axis  is  a  little  over  iy6-  inches  below  the  bottom 
of  the  slab.  The  center  of  action  of  the  concrete  is  always  taken  at 
one-third  of  the  distance  kd  from  the  top,  so  this  brings  the  center  of  the 
compressive  area  one-third  of  5.16,  or  1.72  inches  from  the  top,  and  makes 
the  distance  D  =  20.28  inches. 

[  163  ] 


In  order  to  determine  the  resisting  moment  of  the  beam  with  refer- 
ence to  the  steel  reinforcement,  the  formula 

Ms  =  a  s  D 

is  used,  and  by  substitution 

Ms  =  20.28  X  8  X  16,000  =  2594,840  inch-pounds. 


More  Accurate  Method  of  Determining  the  Resistance  of  Concrete 
to  Compression  in  a  T-section. — After  the  neutral  axis  has  been 
located  in  a  T-section,  as  illustrated  in  Fig.  97,  it  is  known  that  the 
minimum  stress  in  the  section  is  zero  at  the  neutral  axis,  and   maxi- 


-X 


r- 


l 


I 


pq«M«Wi«q 


V 


&-/'^<?.-/co. 


IZ"  -» 


^—34- -§ H 


BaKs^ 


-iz"-A 

Fig.  97 


<6 


■■        M 


J_L__ 


•-vt 


mum  at  the  extreme  top  surface  of  the  slab.  The  entire  resistance  of  the 
portion  of  the  concrete  of  the  beam  section  in  compression  may  then  be 
found  by  taking  the  area,  which  is  stippled  in  the  figure,  at  the  average 
stress  of  300  pounds,  and  by  taking  the  two  side  sections  of  the  T,  which 
are  shown  in  the  figure  by  the  cross-section  lining,  at  the  average  stress 
which  exists  in  these  sections.  This  average  stress  is  greater  than  300 
pounds  if  the  neutral  axis  falls  below  the  bottom  of  the  slab,  and  is  equal 
to  300  pounds  if  the  neutral  axis  coincides  with  the  line  of  the  bottom 
of  the  slab.  Therefore,  where  the  neutral  axis  falls  below  the  bottom 
of  the  slab  it  is  necessary  to  determine  the  average  stress  in  the  two  side 

I  164  ] 


sections  of  the  T.  The  allowable  maximum  compression  at  the  top  of 
the  slab  is  600  pounds  per  square  inch,  and  the  total  allowable  compres- 
sion at  any  section  of  the  slab  is  in  direct  proportion  as  its  distance  varies 
from  the  top  of  the  slab  toward  the  neutral  axis;  so  that  the  maximum 
allowable  stress  on  any  line  between  the  neutral  axis  and  the  top  of  the 
slab  may  be  determined  by  the  proportion  expressed  in  the  following 

equation: 

k, 

Ci=      c 
k 

in  which  Ci  =  the  unit  stress  at  any  line  above  the  neutral  axis. 

ki  =  the  ratio  of  the  distance  between  the  neutral  axis  and  the 

line  at  which  it  is  desired  to  obtain  the  stress,  to  the  total 

depth  of  the  beam, 
k   =  the  ratio  of  depth  of  neutral  axis  to  effective  depth  of  the 

beam, 
c   =the  allowable  unit  stress  at  the  extreme  top  edge  of  the 

beam. 

From  this  the  average  stress,  or  ca,  for  the  two  side  sections  of  the 
T  can  be  obtained  by  the  formula 

k,  , 
c— +c 

Ca=-k 


To  illustrate  the  method  by  which  it  is  determined  whether  there  is 
sufficient  concrete  in  compression,  the  following  example  is  given: 

Example :  Determine  whether  there  is  sufficient  concrete  in  compres- 
sion, at  the  allowable  unit  stress  of  600  pounds,  in  the 
beam  section  illustrated  in  Fig.  97,  to  equal  the  resistance 
of  the  steel  when  stressed  to  16,000  pounds. 

Solution:  The  conditions  of  the  problem  are  illustrated  in  Fig.  97; 
the  total  compressive  resistance  of  the  portion  of  the 
rectangular  section  shown  dotted  above  the  neutral  axis 
is  equal  to 

5.16  X  12  X  300=18,576  pounds; 
[  165  ] 


The  average  stress  in  the  two  side  sections  of  the  T, 
applying  the  above  formula 

c  k+c 
which  by  substitution  becomes 


1.16 
5.16 
ca= ~ =367  pounds. 


600  _—g  +600 


The  area  of  the  two  sections  is  68  X  4,  or  272  square 
inches,  and  their  total  resistance  to  compression  is  272  X 
367=109,824  pounds;  then,  by  adding  together  the 
resistance  of  the  portion  of  the  rectangular  section  shown 
dotted,  and  the  resistance  of  the  two  side  sections  shown 
cross-section,  the  total  resistance  of  the  concrete  in  com- 
pression when  stressed  up  to  the  maximum  of  600  pounds 
at  the  extreme  top  edge,  is  equal  to  109,824+18,576,  or 
128,400  pounds. 

Comparing  this  resistance  to  direct  stress  in  compression,  with  the 
allowable  resistance  of  the  steel,  it  will  be  seen  that  the  8  square  inches 
of  steel  at  16,000  pounds  has  a  resistance  of  128,000  pounds,  so  that  the 
concrete  in  compression  is  more  than  sufficient,  and  no  further  attention 
need  be  given  to  these  portions  of  the  problem. 

It  is  usual  in  the  design  of  reinforced  concrete  to  have  available 
tables  which  give  the  resisting  moment  of  beams  and  girders  of  different 
depths,  reinforced  with  different  areas  of  steel,  and  monolithic  with 
slabs  of  different  thicknesses.  From  such  tables  it  is  very  convenient 
to  select  a  beam  section  which  will  give  the  required  resistance.  This 
can  be  done  by  inspection,  and  no  calculation  is  required  except  to  deter- 
mine the  bending  moment  on  the  beam.  It  is  usual  in  such  tables  to 
show  by  a  line  running  through  the  table  the  demarcation  between  the 
portion  of  the  table  wherein  the  resisting  moments  are  limited  by  the 
steel  from  those  values  in  the  table  which  are  limited  by  the  concrete  in 
compression.  Still  more  convenient  and  desirable  in  the  design  of  con- 
crete houses  are  tables  giving  the  resisting  moments  of  slabs  of  different 
thicknesses,  reinforced  with  bars  and  rods  of  different  sizes  and  spacings. 

(  166] 


Such   tables  and   the   accompanying  explanations   regarding   their 
use  are  given  on  page  192. 


Plan 


Resistance  of  Concrete  Posts  or  Columns. — From  extensive  experi- 
ments upon  full-sized  sections  of  reinforced  concrete  posts  or  columns  it 
has  been  found  that  the  use  of  longitudinal  rein- 
forcing rods  properly  tied  in  with  wire  ties  add 
materially  to  the  strength  of  the  concrete,  so  that, 
while  plain  concrete  in  posts  up  to  15  diameters  in 
length  could  not  be  considered  as  capable  of  sup- 
porting safely  more  than  350  pounds  to  the  square 
inch,  conservative  practice  concedes  that  rein- 
forced concrete  columns  can  safely  sustain  500 
pounds  to  the  square  inch  of  section. 

In  the  several    first-class  cities  the  values 
allowed  upon  reinforced  concrete  columns  vary 
considerably,  but  conservative  prac- 
tice allows  the  use  of  500  pounds  to    -4"  ^4-"5q.    - 
the  square  inch  when  columns  are  re-   lonej/TC/o'/ffd/ 
inforced  with  steel  the  area  of  which  is    Bsrs  <§"  3//£ 
from  1  to  1  Y2%  of  the  area  of  the  con-    or  fa" round 
crete  for  the  longitudinal  rods  or  bars    /rorJ  LoopfJes 
for  columns  whose  length  does  not  ex- 
ceed 15  diameters.     It  is  seldom  that 
concrete  columns  are  used  in  building 
construction  where  the  proportion  of 
length    is   greater    than    this.       If    it 
should  be,  the  safe  strength  per  square 
inch  should  be  reduced  in  proportion 
as  the  length  exceeds  the  diameter  of 
15  to  1. 


1 1  .    - 

'  1  ■  . 

\t  ■       •      . 

ii  •  •  .  -  . 
1  1  .  .   •• 

U*  .  *  • 

J 1    -  •"""  I 


4-' 


* 


Fig.   98. 


E/ev&f /'<?/? 

Method    of  tying   together   vertical 
column  reinforcing. 


Example:   Assume  that  it  is  desired   to  support  a  load  of  80,000 
pounds  on  a  reinforced  concrete  column. 

[167  I 


Solution:    The  safe  unit  stress  is  500  pounds;   therefore  the  area  of 
column  required  equals 

80,000-^-500,  or  160  square  inches; 
A  column  13"  square  would  have  a  sectional  area  of  156 
square  inches,  which  is  sufficiently  close  to  the  required 
result  to  be  used. 

To.  reinforce  this  column  with  1%  of  steel  would  require  a  total 
sectional  area  of  steel  rods  for  longitudinal  reinforcement  equal  to  1.56 
square  inches,  which  divided  among  4  rods  would  give  for  the  area  of 
each  rod  or  bar  .39  square  inch.  The  sectional  area  of  a  %-inch  round 
rod  is  .45;  therefore  four  rods  of  this  size  could  be  used  and  should  be 
placed  and  tied  together  as  indicated  in  Fig.  98. 

In  order  that  the  strength  of  reinforced  columns  of  any  size  may  be 
conveniently  found,  the  following  table  is  given.  This  table  gives  the 
strength  of  the  several  sized  columns  for  the  allowable  unit  compressive 
stresses  on  reinforced  concrete  columns. 


TABLE  6— SAFE  LOADS   IN   POUNDS  FOR  DIFFERENT  UNIT  STRESSES 
ON  SQUARE  REINFORCED  CONCRETE  COLUMNS 


A  rea  of  Steel  in 

Area  in 

350  pounds 

500  pounds 

650  pounds 

750  pounds 

sq.  inches 

Size 

Sq.  Inches 

per  sq.  inch 

per  sq.  inch 

per  sq.  inch 

per  sq.  inch 

of  Column 

Load 

Load 

Load 

Load 

1% 

l\% 

8x    8 

64 

22,400 

32,000 

41,200 

48,000 

.64 

.96 

9x    9 

81 

28,400 

40,500 

52,700 

61,000 

.81 

1. 21 

10  x  10 

100 

35.000 

50,000 

65,000 

75,000 

1. 00 

1.50 

II  X  II 

121 

42,400 

60,500 

78,700 

91,000 

1. 21 

1.81 

12  X  12 

144 

50,400 

72,000 

93,600 

108,000 

1.44 

2.16 

13X13 

169 

59,200 

84,500 

109,900 

126,000 

1.69 

2-53 

I4X  14 

196 

68,600 

98,000 

127,400 

147,000 

1.96 

2.94 

15X15 

225 

78.800 

112,500 

146,500 

169,000 

2.25 

3-37 

16  x  16 

256 

89,600 

128,000 

166,400 

192,000 

1     2.56 

3-84 

17X17 

289 

101,200 

144.500 

187,900 

216,000 

2.89 

4-33 

i8x  18 

324 

113,400 

162,000 

210,600 

243,000 

3-24 

4.86 

19  x  19 

361 

126,400 

180,500 

234,700 

271,000 

3-61 

540 

20  x  20 

400 

140,000 

200,000 

260,000 

300,000 

4.00 

6.00 

21  X2I 

441 

154,400 

220,500 

286,700 

337,000 

4.41 

6.61 

22  X22 

484 

169,400 

242,000 

314,600 

363,000 

4.84 

7.26 

Strength    of    Steel    Columns    Considering  the  Resistance  of  the 
Reinforcement. — In  some  sections  of  the  country  it  is  the  practice  to 

[  168  1 


3 

u 

s 


fcj    ,c 


>     "IS 


~     o.o 


e^: 


include  in  the  calculations  for  determining  the  strength  of  reinforced 
concrete  posts  the  strength  of  the  steel  in  the  longitudinal  rods.  Such 
formulas  are  based  on  the  assumption  that  the  steel  is  subjected  to 
the  corresponding  stress  due  to  its  proportional  deformation,  fixed  by 
the  deformation  of  the  concrete  under  its  safe  stress. 

The  relative  strains  and  stresses  for  the  two  materials  are  expressed 
by  the  ratios  of  the  moduli  of  elasticity,  which  for  stone  concrete  is  taken 
at  from  12  to  15.  The  formula  for  the  strength  of  columns  on  these 
assumptions  is  then  as  follows: 

P  =  c  (A-a)+a  n  c 
In  this  formula 

P  =  safe  bearing  strength  of  the  column. 

A  =  area  of  column  section. 

a  =  sectional  area  of  all  of  the  longitudinal  reinforcing  bars. 

c  =safe  compressive  strength  of  the  concrete. 

n  =  ratio  of  the  moduli  of  the  elasticity. 

It  is  safe  in  using  such  a  formula  to  take  n  at  12,  and  c  at  500  pounds. 

Example:  Assume  that  it  is  desired  to  find  the  safe  strength  of  a 
reinforced  concrete  column  14  inches  square,  reinforced 
with  4  1 -inch  round  bars. 

Solution:    The  total  area  of  the  column  section  is  14"  x  14",  or  196 
sq.  in.,  and  the  total  area  of  the  steel  reinforcement  is 
.78  X  4,  or  3.12;   by  substitution  in  the  above  formula 
P  =  500  (196— 3.I2)+3.I2  X  12  X  500  =  115,160  pounds.     Answer. 

Live  and  Dead  Loads. — In  all  buildings,  whether  dwelling  houses  or 
those  of  larger  and  heavier  construction,  the  design  of  the  floors  and 
walls  depends  upon  the  weights  or  loads  they  will  bs  required  to  sustain. 

In  dwelling  houses  walls  of  ordinary  construction  are  generally  of 
ample  strength  to  carry  the  weight  or  load  usually  imposed.  In  the 
matter  of  floors  and  roofs,  these  can  be  directly  proportioned  and  re- 
inforced to  their  weights  and  the  loads  they  are  required  to  sustain. 

The  architectural  designer  has  to  do  with  two  kinds  of  weights  or 
loads,   namely,   the  weight   of  the   materials  composing   the  structure 

[  171  1 


itself,  and  the  weight  or  load  applied  or  superimposed  upon  the  floors. 
These  two  loads  are  designated  as  the  dead  and  live  loads  respectively. 

Dead  Load. — The  weight  of  the  materials  composing  a  floor  or  roof 
makes  up  the  dead  load,  and  it  is  generally  the  practice  to  reduce  both  the 
dead  and  live  loads  to  the  weight  in  pounds  distributed  over  a  square 
foot  of  surface,  so  that  when  either  a  ' 'dead "  or  "live "  load  is  mentioned 
it  is  understood  to  be  the  weight  in  pounds  per  square  foot  of  floor  area. 
There  would,  of  course,  be  an  exception  where  one  was  considering  a 
load  upon  a  column  or  post,  in  which  case  the  aggregate  dead  and  live 
loads  might  be  meant. 

In  order  to  accurately  determine  the  dead  load  the  designer  must 
know  the  weights  of  the  materials  entering  into  the  construction,  and 
these,  for  dwellings  of  reinforced  concrete,  would  be  as  follows: 


TABLE  7.— WEIGHT  OF  BUILDING  MATERIALS 

Reinforced  Concrete  Weighs  150  Pounds  per  Cubic  Foot 

Cinder  Concrete  Weighs  90  Pounds  per  Cubic  Foot 

Reinforced  Concrete  Slab 

Miscellaneous  Material 

Thickness  in  Inches 

Weight  per  Square 
Foot  in  Pounds 

Material 

Weight  in  Pounds 
Square  Foot 

14 
13 

per 

3 
lXA 

37'A 
43H 

2  Inch  Cinder  Concrete 

with  Sleepers 

2  Inch  Cement  Top 

Coat 

4 
5 

5o 

62  y2 

|  Yellow  Pine  Flooring 

j   Hardwood  Flooring 

Slag  Roof 

Slate  Roof 

Metallic  Lath  and 

Cement  Plaster 

Sheet  Copper  Roofing 

Interlocking  Tile 

3 

4 

6 

8  to  10 

10 

2 
18 

Flat  Promenade  Tile 

16 

It  is  usually  safe  in  house  construction,  where  there  are  reinforced 
concrete  beams  and  girders,  to  take  the  dead  load  of  the  floor  construc- 
tion at  from  90  to  100  pounds  per  square  foot,  and  for  hollow  terra-cotta 

[  172  1 


tile  and  concrete  joist  construction,  to  take  the  live  load  at  from  75  to 
80  pounds. 

Live  Load. — The  live  load  in  any  building  is  an  assumed  weight 
per  square  foot  of  floor  area  which  is  considered  to  be  the  extreme  possible 
limit  of  the  superimposed  floor  loading,  such  as  the  weight  of  the  people, 
furniture  and  merchandise,  and,  in  some  cases,  even  partitions,  if  there 
is  a  possibility  that  the  location  of  these  may  be  changed  to  suit  the 
requirements  of  tenants. 

In  dwelling-houses  the  live  load  per  square  foot  of  floor  surface  is 
very  little — probably  not  actually  amounting,  under  ordinary  conditions, 
to  more  than  10  or  15  pounds  per  square  foot.  In  all  dwelling-houses, 
however,  there  is  the  possibility  of  a  great  number  of  people  being 
assembled  on  the  floors,  and  consequently  in  the  larger  cities  a  live  load 
of  70  lbs.  is  generally  stipulated  in  building  laws  as  being  the  proper 
superimposed  weight  for  designing  the  floor  construction.  This  load 
is  rarely,  if  ever,  realized  and  a  load  of  40  pounds  per  square  foot  is 
ample  for  the  design  of  concrete  houses  not  subjected  to  the  requirement 
of  municipal  building  laws. 

The  combination  of  the  live  and  dead  loads  gives  the  total  load  per 
square  foot  of  floor  area.  The  average  total  floor  load  for  a  dwelling- 
house,  considering  a  live  load  of  40  pounds,  would  seldom  be  over  120 
to  130  pounds  per  square  foot. 

Roof  Loads, — In  modern  structures  of  considerable  size  it  is  some- 
times considered  essential,  in  designing  the  roofs,  to  make  allowance  for 
snow  and  wind  loads.  Generally  in  the  design  of  smaller  buildings, 
which  classification  would  include  dwellings,  even  pretentious  types, 
it  is  usual  to  combine  the  snow  and  wind  loads,  and  to  use  a  superim- 
posed load  on  the  roof  of  from  25  to  30  pounds  per  square  foot.  This 
load  added  to  the  weight  of  the  roof  construction  gives  the  total  roof 
load  per  square  foot. 

In  climates  comparatively  temperate  the  load  of  25  to  30  pounds 
could  be  reduced  to  from  15  to  20  pounds  unless  it  was  proposed  to  use 

[  i73  1 


the  roof  as  a  promenade,  when  it  would  be  safer  to  use  a  somewhat 
heavier  superimposed  load.  Roofs  that  are  very  steep  have,  of  course, 
little  snow  load,  but  on  the  other  hand  the  wind    pressure   increases. 

Weights  on  Floor  Slabs,  Beams,  Girders,  etc. — In  the  planning 
of  floors  the  floor  slab,  if  of  concrete,  must  be  designed  first.  The  dead 
load  of  the  floor  slab  alone  is  not  as  great  as  the  dead  load  of  the  entire 
floor  construction,  so  that  in  order  to  get  a  total  load  per  square  foot  on 
a  floor  slab  the  live  load  is  added  to  the  actual  weight  of  the  floor  slab 
and  the  finished  floor,  whatever  that  may  be. 

The  total  load  per  square  foot  upon  a  beam  or  girder  must  take  into 
account  the  weight  of  the  beam  or  girder  itself,  distributed  over  the 
floor  area  which  it  supports,  and  this  dead  load  is,  of  course,  somewhat 
more  than  the  dead  load  of  the  slab  itself.  The  total  weight  that  a  beam 
or  girder  supports  is  equal  to  the  area  of  floor  carried  by  it  multiplied  by 
the  total  floor  load,  which  includes  the  dead  and  live  loads,  and  in  the 
same  manner  we  calculate  the  load  carried  by  a  column  or  post,  with 
the  exception  that  if  it  carries  more  than  one  floor  the  aggregated  weight 
from  all  floors  which  the  column  supports  must  be  taken. 

Usually  the  area  supported  by  a  beam  or  girder  is  equal  to  the  span 
multiplied  by  the  distance  from  center  to  center  of  these  structural 
members,  and  where  a  girder  supports  a  number  of  reinforced  concrete 
beams  it  is  usual  to  figure  the  girder  as  being  uniformly  loaded  rather 
than  as  supporting  a  number  of  concentrated  loads.  This  is  owing  to 
the  monolithic  character  of  the  construction,  the  weight  from  the  beams 
being  well  distributed  over  the  girder. 


f  174 


Chapter  VI 

Calculating  the  Bending  Moments  for  Reinforced 
Concrete  Beams  and  Slabs,  and  the  Determina- 
tion of  Size  and  Reinforcement 


Chapter  VI 

Calculating  the  Bending  Moments  for  Reinforced  Concrete 

Beams  and  Slabs,  and  the  Determination  of  Size 

and  Reinforcement 

Theory  of  Bending  Moments. — The  loads  on  a  beam  produce  trans- 
verse stress  on  the  material  composing  the  beam.  The  loads  and 
the  reaction  at  the  supports  act  about  any  point  in  the  length  of  the  beam 
through  lever  arms  equal  to  the  perpendicular  distance  from  the  line  of 
action  of  the  load  or  the  reaction,  and  both  the  loads  and  the  reactions 
produce  moments  about  any  point.  These  moments  are  either  positive 
or  negative,  as  they  act  together  or  in  opposition  to  each  other.  It  is 
evident,  therefore,  that  the  moments  which  act  in  the  same  direction 
may  be  added  together,  and  that  those  which  are  opposed  may  be  deducted 
from  the  sum.  In  this  way  the  algebraic  sum  of  the  moments  about  any 
point  in  the  length  of  a  beam  may  be  obtained,  and  the  resultant  moment 
is  called  the  bending  moment.  This  bending  moment  is  resisted  by  the 
strength  of  the  material  of  which  the  beam  is  composed,  so  that  in  order 
to  determine  whether  a  beam  is  of  sufficient  section  to  resist  the  action 
of  the  loads  and  the  reactions,  it  is  necessary  to  find  the  maximum  or 
greatest  bending  moment  to  which  the  beam  is  subjected. 

Formulas  for  Greatest  Bending  Moments  on  Simple  Beams. — 
The  greatest  bending  moment  on  any  simple  beam  may  be  determined 
by  finding  the  algebraic  sum  of  the  moments  about  the  point  at  which 
the  greatest  bending  moment  occurs. 

For  convenience  it  is  customary  to  use  simple  formulas,  arranged 
in  terms  of  the  weight  and  span,  for  finding  the  bending  moment  on 

12  [   177  1 


beams  loaded  with  a  uniformly  distributed  load,  a  load  concentrated  at 
the  center,  or  a  triangular  shaped  load  such  as  the  weight  of  brickwork 
on  a  lintel  over  an  opening. 

In  the  following  tabulation  a  simple  beam  is  considered  as  one 
supported  at  both  ends,  while  a  cantilever  is  a  projecting  beam  or  one 
supported  at  one  end  only.  In  the  formulas  the  bending  moment,  M, 
is  determined  in  inch-pounds,  the  weight,  W,  is  taken  in  pounds,  and  the 
span  in  feet  or  inches  as  designated  L  or  1,  respectively. 

FORMULAS  FOR  BENDING  MOMENTS 

Wl 
Simple  Beam,  Uniform  Load M  —  ~g~  or  1.5  WL 

Wl 
Simple  Beam,  Load  Concentrated  at  the  Center M  =— -  or     3  WL 

Wl 

Simple  Beam,  Triangular  Load,  Apex  at  the  Center M  =  -y-  or      2  WL 

Wl 
Simple  Beam,  Uniform  Load;  Ends  of  Beam  Hxed M  =~T~  or  1.2  WL 

Wl 
Cantilever  Beam,  Uniform  Load M  =         or     6  WL 

Cantilever  Beam,  Load  Concentrated  at  End M  =W1  or    12  WL 

Example:  What  will  be  the  greatest  bending  moment  of  a  rein- 
forced concrete  floor  beam  which  has  a  span  of  20  feet, 
and  where  the  distance  from  center  to  center  of  beam  is 
6  feet,  and  the  total  load  140  pounds  per  square  foot? 

Solution:    The  area  of  floor   supported  is  equal  to  6X20,  or  120 

square  feet,  and  the  total  load  on  the  beam  consequently 

equals  120  X  140,  or  16,800  pounds.     Considering  that 

the  beam  will  be  taken  as  fixed  at  the  ends,  the  formula 

for  a  uniform  load  with  the  ends  fixed  will  be  applied. 

This  formula  gives  the  value  of 

Wl 
M=         or  1.2  WL, 

so  that  by  the  substitution  of  the  values  in  the  formula 
M  =  i.2  X  16,800  X  20  =  403,200  inch-pounds. 


Application    of   Formulas    to    Reinforced    Concrete    Beams. — The 
factor  of  safety  used  for  reinforced  concrete  is  large — that  is  to  say, 

[178] 


while  in  figuring  the  resistance  of  the  material  it  is  customary  to  use 
factors  of  safety  of  four,  for  the  steel  and  concrete,  there  are  certain 
assumptions  made  with  reference  to  the  method  of  figuring  the  bending 
moments  which  are  so  far  within  the  safe  limits  that  under  any  ordinary 
conditions  of  fair  design  and  workmanship  the  actual  bending  moment 
is  so  reduced  as  to  give  a  much  greater  factor  of  safety  than  is  usual  in 


0.    :&  A  *< 

V*  >  a  4 

>  aA- 


r  a-  •.»£ >„■  a; 
kb*'  t>    &  *  A 

■  i'r'P  ••• 
'>>'  A  * 


Load  co*7£>/tffe'r<?v/  <2cJ//ip  fev/97  fece  £?  fece  a/  3*&/f7& 

W/ 


Fig.  99. 


L  Odd  £0*7&/dfcr<&/  JcJ/ina  /ra/7?  tfrt/rs  -/a  cf/7/re  0/  fisjmg 

/o 

Fig.  100. 


v&tr 


structures  subjected  to  static  loads.  The  principal  reason  for  the 
increase  in  the  factor  of  safety  in  reinforced  concrete  construction  lies 
in  the  fact  that  the  entire  system  of  beams  and  girders,  together  with  the 
floor  slab,  is  usually  monolithic,  and  the  girders  and  beams,  besides  being 
continuous  over  several  supports,  act  mutually  in  two  directions,  thus 
adding  greatly  to  the  strength  of  the  floor  system.     (See  Fig.  99.) 

[i79] 


The  conservative  practice  in  the  design  of  reinforced  concrete  floor 
slabs  is  to  figure  the  bending  moment  by  the  formula  —  when  the  loads 
and  spans  are  considered  as  acting  over  a  distance  equal  to  the  distance 
from  center  to  center  of  beams,  and  to  use  the  formula  -«-  when  the 
clear  span  of  the  slab,  or  the  distance  from  face  to  face  of  beam,  is  taken 
as  the  span,  and  the  distance  over  which  the  load  is  distributed.  These 
two  assumptions  are  illustrated  in  Fig.  ioo.  There  is  generally  some 
economy  gained  by  using  the  first  formula,  but  when  this  formula 
is  used,  the  reinforcing  rods  should  be  brought  to  the  top  of  the  slab 
over  the  beam  bearings. 

In  the  design  of  beams  and  girders  it  is  undoubtedly  safe  to  consider 
them  as  fixed  at  the  ends,  and  to  therefore  figure  the  bending  moment 
upon  them  by  the  formula  — .  Where  this  formula  is  used  the  span  of 
the  beam  and  girder  should  always  be  taken  as  the  distance  from  center 
to  center  of  supports,  even  though  only  the  load  which  would  be  supported 
by  the  clear  span  is  considered. 

As  in  slab  construction,  the  beams  and  girders  should  never  be 
considered  as  fixed  at  the  ends  unless  they  are  monolithic  at  the  points 
of  support  with  the  floor  construction,  or  else  are  securely  built  into  the 
walls,  and  then  only  when  the  reinforcing  rods  are  bent  up  toward  the 
supports  to  form  reinforcement  for  the  change  in  the  bending  moment 
which  takes  place  in  continuous  beams  over  supports.  The  method  of 
figuring  bending  moments  for  slabs,  beams,  and  girders,  and  the  partic- 
ular formula  which  may  be  used,  is  usually  regulated  by  the  building 
laws  in  cities  of  the  first  class.  Outside  of  the  scope  of  such  laws  the 
designer  can  use  such  modifications  of  these  formulas  as  his  judgment 
and  experience  may  dictate.  Where  the  material  and  workmanship  are 
of  first  quality,  the  designer  can  certainly  afford  to  use  those  assumptions 
which  will  give  him  the  most  economical  results,  and  still  be  assured  of 
having  a  secure  and  safe  building,  for  the  reasons  stated  above. 

Minimum  Depths  of  Slabs,  Beams,  and  Girders. — In  the 
design  of  reinforced  concrete  structures  there  are  certain  minimum 
thicknesses  for  slabs,  and  depths  for  beams  and  girders,  which  are  uni- 

[  180I 


versally  adhered  to.  For  instance,  it  is  considered  impractical  to  build 
a  reinforced  concrete  slab  between  beams  of  less  than  3  inches  in  total 
thickness,  and  it  is  best,  in  any  case,  not  to  make  the  slab  less  in  thick- 
ness than  two-fifths  of  an  inch  for  each  foot  in  span.  For  example,  assume 
that  the  span  of  a  slab  between  beams  is  8  feet:  if  two-fifths  of  an  inch 
is  allowed  for  each  foot  of  span,  and  the  span  is  8  feet,  this  would  give  a 
thickness  of  sixteen-fifths,  which  is  3^  inches,  and  the  slab  would  be 
made  3J/2  inches  in  thickness. 

It  is  customary  in  designing  beams  and  girders  to  confine  the  mini- 
mum depth  of  the  beam  or  girder,  counting  from  the  under  side  of  the 
slab  to  the  bottom  of  the  member,  as  three-fifths  of  an  inch  for  each  foot 
in  span.  To  illustrate,  assume  that  a  beam  has  a  span  of  20  feet;  allow- 
ing three-fifths  of  an  inch  for  each  foot  in  span  would  make  the  minimum 
depth  of  the  beam  sixty-fifths,  or  12  inches,  which  would  be  shallow 
enough  for  a  beam  of  this  span  supporting  any  kind  of  a  load. 

In  deciding  on  the  depth  of  beams  and  girders  the  commercial  width 
of  lumber  from  which  the  forms  are  to  be  made  should  be  taken  into 
account,  unless  it  is  proposed  to  saw  and  work  stock  boards  to  the 
necessary  width.  It  is  only  by  such  care  that  the  best  economy  is 
attained  in  the  construction  of  concrete  dwellings. 

The  Minimum  Width  of  Beams  and  Girders. — There  are  three 
factors  which  regulate  the  width  of  beams  and  girders  of  reinforced 
concrete  : 

First:  The  minimum  space  into  which  reinforcing  rods  can  be 
placed  and  into  which  concrete  may  be  poured  and  spaded 
or  tamped. 

Second:  The  minimum  width  that  will  allow  the  steel  to  be  suffi- 
ciently fireproofed. 

Third:  The  minimum  amount  of  concrete  around  the  reinforcing 
rods  or  bars  that  will  develop  their  resistance. 

It  is  seldom  practical  to  make  reinforced  concrete  beams  less  than 
6  inches  in  width,  and  they  may  be  as  much  wider  as  is  needed  to 
meet  the  requirements  above  stated,  or  as  may  be  necessary  for  archi- 

[•83] 


tectural  appearances.  In  all  instances  there  should  be  at  least  I  Yi  inches 
of  concrete  outside  of  the  steel  reinforcement  on  both  sides  and  bottom 
of  the  beam  to  give  the  necessary  protection  in  the  way  of  fireproofing, 
and  it  is  also  considered  good  practice  to  allow  a  distance  from  center 
to  center  of  the  reinforcing  rods  or  bars  of  at  least  2Y2  times  the  diameter 
of  the  rod  or  bar. 

Determining  the  Bending  Moment  on  Square  Slabs. — In  figur- 
ing the  bending  moments  on  slabs,  whether  they  span  from  wall 
to  wall  unsupported  by  beams,  or  are  incorporated  with  beams  and, 
being  monolithic  with  them,  form  a  T-section,  it  is  always  customary  in 
figuring  the  load  and  the  bending  moment  to  consider  a  portion  of  the 
slab  i  foot  in  width. 

The  difference  between  slabs  and  beams  and  girders,  with  reference 
to  the  bending  moment,  exists  in  the  fact  that  the  slabs  may  be  supported 
on  four  sides  and  be  reinforced  in  two  directions.  Where  it  is  possible 
to  reinforce  a  slab  in  two  directions,  considerable  economy  can  be  exer- 
cised from  the  fact  that  the  bending  moment  in  either  direction  is  mate- 
rially reduced,  and  consequently  the  slab  need  not  be  so  thick,  and  sup- 
porting beams  may  be  omitted.  Where  the  slab  is  square,  and  is  sup- 
ported on  all  four  sides  in  a  secure  and  fixed  manner,  then  the  bending 
moment  on  the  slab  may  be  found  by  the  following  formula: 

WL 

M  (foot-pounds)  —   __ 

or,  if  the  span  is  in  feet  and  the  resulting  bending  moment  is  in  inch- 
pounds, 

3WL 

M  (inch-pounds)  —      _ 

To  illustrate  the  application  of  this  formula,  assume  that  it  is 
desired  to  find  the  bending  moment  created  in  a  floor  slab  12  feet  square, 
and  supporting  a  total  uniformly  distributed  load  of  125  pounds.  The 
load  on  a  portion  of  the  slab  1  foot  in  width  is  equal  to  12  X  125,  or  1500 
pounds.     Applying  the  above  formula,  and  substituting, 

..     3WL    3X  1500X12 

M= — —  =  —  =  10,800  inch-pounds. 

[184] 


By  referring  to  Table  9  it  will  be  observed  that  a  slab  with  a  total  thick- 
ness of  5  inches,  reinforced  with  ^-inch  square  twisted  bars,  spaced 
4  inches  center  to  center,  will  give  the  required  resistance ;  the  reinforce- 
ment must,  of  course,  extend  in  both  directions. 

Double  Reinforcement  in  Rectangular  Slabs. — Floor  slabs  which 
are  supported  on  four  sides,  but  which  are  rectangular  instead  of 
square,  may  be  reinforced  lengthwise  and  crosswise;  the  reinforce- 
ment running  crosswise  of  the  beam  must  be  heavier  than  that  running 
lengthwise,  from  the  fact  that  the  greater  proportion  of  the  load  will  be 
carried  by  the  short  span.  This  is  best  explained  by  the  fact  that  the 
stress  in  steel  or  concrete,  or  in  fact  any  material,  is,  within  working 
stresses,  always  proportional  to  the  amount  of  strain  or  deformation  pro- 
duced in  the  material.  It  is  consequently  evident  that  the  greatest  strain 
will  be  produced  in  the  reinforcement  running  the  short  way  of  the  slab 
when  subjected  to  the  same  deflection,  as  the  reinforcement  running  length- 
wise. In  rectangular  slabs,  therefore,  it  is  necessary  to  figure  the  amount  of 
reinforcement  required  in  both  directions,  by  figuring  the  bending  moment 
created  in  the  slab,  with  regard  to  both  short  and  long  span. 

TABLE   8.— PROPORTION   OF   LOAD    CARRIED    IN    BOTH    DIRECTIONS 
BY  RECTANGULAR  FLOOR  SLABS 

Ratio  of  Length  of  Proportion  of  Load  Carried  Proportion  of  Load 

Slab  to  Breadth  by  Reinforcement  of  Carried  by  Long 

Short  Span  Span 


1    5   • 

1.1 6   . 

1.2 67. 

1.3 74- 

i-4 79 

1.5 83. 

1.6 87. 

1.7 89. 

1.8 91 . 

1-9 93 

2     94 


The  proportionate  part  of  the  total  load  on  a  rectangular  floor  slab 
which  will  be  carried  by  the  reinforcement  extending  the  short  way  of 
the  slab,  can  be  found  by  the  following  formula: 

1< 


LD  = 


185  1 


In  this  formula 

Lp  =  the  proportion  of  the  load  resisted  by  the  reinforcement  placed 

the  short  way  of  the  slab. 
1     =  the  length  of  the  slab, 
w   =  the  breadth  of  the  slab. 

the  value  Lp  is  the  proportional  part  of  the  total  load  per  square  foot. 
In  order  to  save  calculation,  the  various  values  of  Lp,  or  the  proportional 
part  of  the  load  carried  by  the  reinforcement  extending  the  short  way  of 
the  beam,  may  be  determined  from  Table  8,  which  has  been  worked 
out  for  proportional  parts  of  length  to  breadth,  varying  by  tenths,  from 
square  slabs  to  rectangular  slabs  having  a  length  equal  to  twice  their 
breadth. 

In  order  to  explain  the  use  of  Table  8  and  the  method  of  calculating 
the  amount  of  reinforcement  required  in  a  rectangular  slab  reinforced  in 
two  directions,  the  following  example  is  given: 

Example:  Determine  the  amount  of  reinforcement  required  both 
crosswise  and  lengthwise,  for  a  reinforced  concrete  slab, 
supported  on  four  sides,  having  a  width  of  io  feet  and  a 
length  of  12  feet. 

Solution:    The  ratio  of  the  length  to  the  breadth  is  as 

1  12 

— i  or  —  =  i.2. 
w '        io 

Referring  to  the  above  table,  it  will  be  found  that  the 
proportional  part  of  the  load  carried  by  the  reinforcement 
extending  across  the  slab  is  .67;  if  therefore,  the  total 
load  is  130  pounds  per  square  foot,  the  proportional  part 
of  this  load  carried  by  the  short  span  will  equal  130  X 
.67  =  87  pounds  per  square  foot.  In  figuring  the  bending 
moment  in  rectangular  slabs,  after  the  proportional  part 
of  the  load  is  found  for  each  span,  the  bending  moment 
is  figured  by  the  formula 

IO 

therefore  the  bending  moment  in  this  instance  will  equal 

870  X  10 

—  =870  foot-pounds,  or  10,440  inch-pounds. 

f  186  1 


By  referring  to  Table  9,  a  4-inch  slab  with  square  bars,  it  will  be 
found  that  f-inch  square  bars  spaced  5-inch  centers  will  give  a  resisting 
moment  of  10,650  pounds,  which  is  only  slightly  in  excess  of  the  require- 
ments, and  is  the  correct  size  to  use. 

Stirrups. — All  concrete  beams,  whether  rectangular  or  T-sec- 
tion,  should  have  secondary  reinforcement  in  the  form  of  stirrups,  which 
extend  from  the  main  reinforcing  rods  or  bars,  vertically  or  diago- 
nally, through  the  web  of  the  beam  to  the  top.  These  stirrups  have  several 
uses,  namely,  they  help  to  transmit  the  stress  in  the  reinforcing  rods  to 
the  portion  of  the  concrete  in  compression  by  resisting  the  horizontal 
shear;  their  greatest  use,  however,  is  to  prevent  what  is  known  as 
diagonal  tension  cracks  near  the  abutments,  or  points  of  support. 

There  are  various  formulas  by  which  the  number  of  stirrups  can  be 
figured,  but  designing  engineers  do  not,  as  a  rule,  apply  them  in  practice, 
and  such  formulas  would  be  particularly  useless  in  the  design  of  concrete 
dwellings,  where  the  loads  are  light.  A  very  excellent  rule,  and  one  which 
is  used  almost  universally  by  designing  engineers  of  considerable  experi- 
ence, is  to  place  in  the  beam  or  girder  stirrups  equal  in  number  to  the 
span  in  feet.  As  the  stirrups  are  primarily  shear  members,  and  as  the 
shear  increases  toward  the  points  of  support  and  is  zero  at  the  center 
of  the  span  of  a  beam  uniformly  loaded,  it  is  customary  to  place  the 
stirrups  close  together  at  the  abutments,  and  farther  apart  toward  the 
center  of  the  span.  An  excellent  rule  is  to  space  the  stirrups  at  the 
abutments  according  to  the  following  tabulation: 

First  three  stirrups  @     4-inch  center  to  center. 
Next  two  stirrups  .  @     6-inch  center  to  center. 

Next  stirrup @  12-inch  center  to  center. 

Next  stirrup @  18-inch  center  to  center. 

The  maximum  distance  for  stirrups  should  not  be  over  three  feet  apart 
at  the  center  of  the  span. 

Stirrups  used  as  the  secondary  reinforcement  for  concrete  beams 
and  girders  in  house  construction  may  be  of  34-inch  diameter  round  rods, 
and  this  size  of  stirrup  is  sufficient  if  spaced  according  to  the  above 
schedule. 

[  187] 


Chapter  VII 

Tables  for  Designing  Reinforced  Con- 
crete   Construction    and    Their    Use 


PQ 


Chapter  VII 

Tables  for  Designing  Reinforced  Concrete  Construction  and 

their  Use 

The  several  formulas  which  have  been  given  for  finding  the  location 
of  the  neutral  axis  and  the  resistance  of  reinforced  concrete  beams, 
involve  more  or  less  lengthy  calculations,  so  that  it  is  usual  to  employ 
tables  which  give  the  results  of  many  calculations  based  on  the  formulas. 

One  of  the  most  valuable  of  these  tables  gives  the  resistance,  or 
resisting  moment,  of  reinforced  concrete  slabs.  The  resisting  moments 
of  reinforced  concrete  slabs  one  foot  in  width  are  given  in  inch-pounds 
in  Table  9.  The  resisting  moment  selected  from  the  table  must  equal 
the  maximum  bending  moment  due  to  the  load  on  the  slab  taken  in  inch- 
pounds.  An  examination  of  this  table  shows  that  it  gives  the  resisting 
moments  for  slabs  from  3  inches  to  6  inches  in  thickness,  varying  by  the 
one-half  inch,  and  reinforced  with  both  square  and  round  bars,  ranging 
from  }/i  inch  to  %  inch,  and  spaced  from  2  inches  to  12  inches  center  to 
center. 

It  will  be  observed  that  an  irregular  line  passes  through  these 
tables.  This  line  separates  the  values  which  are  limited  by  the  steel 
reinforcement  from  those  values  that  are  limited  by  the  resistance  of 
the  concrete  to  compression.  The  values  above  the  line  are  regulated 
by  the  strength  of  the  steel  reinforcement,  while  those  below  the  line 
are  determined  by  the  resistance  of  the  concrete. 

The  nearer  the  values  approach  the  line,  the  more  nearly  are  both 
the  steel  and  the  concrete  subjected  to  their  maximum  working  stresses. 

A  study  of  the  table  will  show  the  values  of  the  resisting  moments 
below  the  line  increasing  in  a  much  less  ratio  than  the  amount  of  steel 
used  for  the  reinforcement,  thus  showing  a  loss  of  economy. 

[191] 


The  values  in  the  following  table  are  based  upon  the  strength  values 
of  stone  concrete,  composed  of  one  part  of  Portland  cement,  two  parts 
of  clean  gravel  or  sand,  and  four  parts  of  good  hard  broken  stone.  The 
allowable  working  stress  of  the  steel  is  taken  at  16,000  pounds  per 
square  inch,  and  the  allowable  compressive  stress  on  the  concrete  at  the 
extreme  fiber  is  600  pounds  per  square  inch.  The  ratio  of  the  moduli 
of  elasticity  of  the  materials  is  taken  at  12.  Attention  is  also  called  to 
the  fact  that  the  fractional  values  in  the  first  column  of  the  table  are  the 
figures  denoting  the  size  of  the  bars — either  the  diameter  of  the  round 
rods  or  the  side  of  the  square  bars.  The  figures  at  the  top  over  each 
column  is  the  spacing  of  the  rods  in  inches,  or,  as  it  is  sometimes  called, 
the  "pitch." 

It  must  be  borne  in  mind  in  selecting  values  from  the  tables  that 
the  nearest  value  within  5%  above  or  below  the  bending  moment  may 
be  used,  and  it  is  generally  considered  best  not  to  use  the  bars  in  sixteenth 
sizes,  but  rather  to  use  those  in  the  eighth  size,  such  as  34,  zA>i  3^,  and  %• 
It  is  good  practice  to  use  the  same  sized  rods  or  bars  throughout  a  job, 
and  rather  to  use  small  bars  at  a  reasonable  spacing  than  the  larger 
bars  at  8",  9",  or  10"  pitch. 


TABLE  9.— RESISTING  MOMENTS  IN   INCH-POUNDS.     IN    EVERY    CASE 
CENTER  OF  STEEL  IS  ONE  INCH  FROM  BOTTOM  OF  SLAB 
[Figured  for  stone  concrete  1-2-4  mixture  16,000  pounds  on  steel  600  pounds  on 
concrete  Phila.  Law.     Below  line,  steel  is  in  excess  of  critical  percentage  and  concrete 
is  limiting  factor.] 

Three-Inch  Concrete  Slabs. 
Round  Rods  Spaced  Center  to  Center. 


Diameter  of  Rods 

2 

ins. 

3 

ins. 

4 
ins. 

4078 
4776 
5332 
5837 
6265 
6620 

5 
ins. 

338o 

6 

ins. 

2818 

7 
ins. 

2396 

3742 

8 
ins. 

2112 
3300 

9 
ins. 

10 

ins. 

1690 
2640 
3802 

11 
ins. 

12 

ins. 

\i  inch 

5155 
5870 
6432 

4507 
5222 
5803 
6288 
6696 

1880 
2927 

I535i  i4°9 

5    " 

is     

441 1 

4973 
5467 
5900 
6280 
6605 

4133 
4709 

5189 
5606 
598o 
6320 
6615 

2400  2200 

a    " 

s     

4430 
4930 
5342 
5730 
6058 
6360 
6635 

4262 
4738 
5150 
5520 
5870 
6172 
6432 

4075 
4541 
4960 

5332 
5673 
598o 
6265 

3452 !  3168 

TV   "   

4377 
4810 

5175 
5500 

5822 
6086 

41761  4118 
4653  4500 
501 1  4895 
5342  5222 

5664   «20 

y2   "   

9  «< 

r 5   

1  "  

\l   "  

%    "   

5937 

5803 

192  ] 


Three-Inch  Concrete  Slabs. 
Square  Bars  Spaced  Center  to  Center. 


inch. 


tV 


'  of  Rods 
J               ins. 

3 

4 

0 

6 

7 

*    9 

w 

//    12 

ms. 

ms. 

4425 
5140 
5730 

ins. 

4I05| 

4800 
536o 

ms. 
3587 

ins. 

ins.     ins. 

ms. 

2152 
3360 

ms. 

1955 

3053 

ms. 

■  ■  •  5532 

.  .  .  6260 

.  .  68(H) 

4900 
5600 
6187 

3050 

2600 

2382 

1794 

4493 
5065 

4264 
4840 

4066 

3734 

2800 

4637 

443" 

4286 

4138  4008 

6658 

6225 

5865 

5568 

5304 

5105  4930 

4766 

4600  4460 

6630 

6293 

5990 

5645 

5534  5342 

5189 

5016  4900 

6648 

6365 

61 10 

59i8  5726J 

5554 

5400  5265 

6686 

6437 
6710 

6260  6058 
6540  6355, 

5900 
6206 

5750  5606 
6038  591 1 

" 

6800  6630 

6460 

6320  6190 

Three  and  One-half 
Round  Rods  Spaced 

Inch  Concrete  Slabs. 
Center  to  Center. 

Diameter  of  Rods 

2 
ins. 

7515 

8593 

95io 

10260 

3 

ins. 

6525 

4     \     5         6 
ins.      ins.      ins. 

7 
ins. 

2995 
4680 

8 
ins. 

9 

ins. 



2350 
3660 

5280 

10 

ins. 

2115 
3300 
4755 

n 

ins. 

1920 
3000 

4315 

5876 

12 
ins. 

l/i  inch 

5284 

4226 

3525 

2640 
4125 
594« 

1760 

5   " 

7620 

6880 

6320 

5505 

2751 

8490:  7770 
9270  8540 

3   " 

«•     

7250 

6810 

6410 
7i5o 
7790 
8385 
8935 
9390 
9835 

3960 

t's   '  

7990  7570 

6840 

7515 
8085 

8595 
9100 

95'o 

6580 

7215 
7770 

8295 
8790 

8225 

h  6315 
"  6940 
7540 
S055 
8510 
8970 

5390 

y2   "   

9930 
10490 

9225 
9820 

10330 

8660 
9260 
9790 
10220 
1 0650 

8210 
8805 
933o 
9800 
10215 

6735 
7300 
7800 
8280 
8720 

6525 
7070 
7620 

8075 
8500 

9  " 

S    «' 

1  1 

H    "   

Three  and  One-half  Inch  Concrete  Slabs. 
Square  Bars  Spaced  Center  to  Center. 


Diameter  of  Rods 


M  inch . 


2 

3 

4 

ms. 

ins. 

ms. 

6410 
7500 

8110 
9210 

7090 
8200 

10095 

91 10 

8385 

i  '  " 

9870 

9160 

10500 

9835 
10380 

5 
ins. 

6 

ins. 

4485 

538o 

6920 

7825 
8595 
9270 
9860 

1 0360 


6505 
7390 
8160 

8815 

9400 

9915 
10375 


7 
ins. 

38i5 
595o 


8 
ins. 

336o 
5250 


9 
ins. 


2975 
4665 


10 

ins. 


6975 
7735 
8405 
9050 
95«o 
9980 
10400 


0705 
745o 
8110 
8680 
9210 
9690 
10095 


6410 
7150 
7790 
8385 
8925 
9390 
9835 


2690 
4200 
6052 


ins. 

2445 
38io 
5500 


6880 
7570 
8140 
8650 

9135 
9560 


6675 
7305 
7875 
8410 
8895 
9315 


12 
ins. 

2240 
3500 
5045 


6465 
7090 
7690 
8200 
8670 
9110 


'3 


193  1 


Four-Inch  Concrete  Slabs. 
Round  Rods  Spaced  Center  to  Center. 


Diameter  of  Rods 


}4  inch 


A 


10130 
1 1 750 

13055 
14160 


8453 


4 

ins. 


6430 


10290 
1 1600 
12700 
13640 
14460 
15190 


9320) 
10580! 
1 1 700 
12610 
1 3460 1 
14220 
14880 


5 

ins. 

5070 
7925 


9785 
10900 
11810 
12680 
13400 


6 
ins. 


4225 
6600 


9170 
10200 
1 1 170 
12000 
12770 


I4"5ji3455 
1 46461 1 4095 


7 
ins. 


3590 
5610 
8080 


8 
ins. 

3165 
495o 
7100 


9700  9230 
1062010130 
11430T1030 
12215.11750 
12875  12420 
i35oo'i3055 


9 

10 

11 

ins. 

ins. 

ins. 

2820 

2535 

2300 

4390 

3960 

3600 

6330 

5680 

5120 

8610 

7750 

6975 

9850 1  9400 
10590  10190 
II300T0960 
1 1970]  1 1630 

12635  12235 


9070 

9860 
10570 
1 1 245 

1 1890 


12 

ins. 

2115 
3300 
4735 
6457 
8440 


959o 
10290 

10995 
1 1600 


Four-Inch  Slabs. 
Square  Bars  Spaced  Center  to 

Center. 

Diameter  of  Rods 

2 
ins. 

3 

ins. 

9612 
1 1 150 
12450 
13590 
14500 
I53IO 

4 
ins. 

5 

ins. 

6         7 
ins.     ins. 

8 
ins. 

9 

ins. 

10 
ins. 

11 

ins. 

12 

ins. 

\i  inch 

1 1030 
12610 
13920 
1 5000 

6070 

6460 

538o  4575 

4033 

3570 
5600 
8070 

3230 
5040 

2930  2690 

S    ' 
T6 

IOIOO 

1 1390 
12540 
13480 
14320 
15030 

937o 
10650 
1 1 750 
12700 
13540 
14270 
14940 

8500;  7140  6300 

4580  4200 

8    ' 
8 

9970 1  9440  9018 
1 1080  105301  IOIOO 
12000  11430111030 
12900;  12290  1 1 850 
13630)13060  12610 

14310  13730  13300 

1 49 1 5  14340  13920 

7260 

6600  6025 

7    ' 
Til 

9580 
10600 
1 1390 
12190 
12870 
13480 

9300 

8990  8240 

9     1 

10200 
1 1050 

9880  9610 

I07AO  IOJ.J.O 

ft     ' 

1 1800  1 1430  1 1 150 
12500  1 2 130  1 1 830 

I"U10  12770  1 2 J. SO 

1  1    ' 

3A    ' 

Four  and  One-half  Inch  Concrete  Slabs. 
Round   Rods   Spaced   Center   to    Center. 


Diameter  of  Rods 

2 

ins. 

3 

ins. 

4 

ins. 

5 
ins. 

5916 
9246 

6 

ins. 

4932 

7704 

1 1090 

7 
ins. 

8 
ins. 

9 

ins. 

10 
ins. 

ins. 

12 
ins. 

14  inch .  . 

I3I35 
15230 
17010 
18510 
19770 
20874 

9864 

7400 

4194 
6550 
9427 

3700 

5775 
8317 

3290 
5123 
7393 

2960 
4620 

6655 
9060 

1 1 833 

2687 

2465 

A  "  -■ 

13320 
15040 
16510 

1 1 557 

4200  3850 

1  "  •• 

13625  12600 
15125  14070 

6042  5545 

A 

1321512435 
14495  13655 
15555  14860 
1 6625  j  1 5845 
1 7580 1 1 6745 
18405  17655 

1 1320  10065 

8225  7560 

M   "  .. 

17845 
19035 
19980 
20874 

1 6405  i  1 5300 

13125  12555 

10750I  9860 

A  "  •• 
1  "  •■ 

H   "   ■■ 

17580 
18595 
19505 
20345 

16480 
17520 

18435 
19300 

14260 

15230 

16155 
17010 

13625 
14700 
15550 
16405 

13185 
14200 
15080 
15935 

12715 
13655 
14635 
15405 

12320 
13320 

M235 
15040 

•94] 


Four  and  One-half  Inch  Concrete  Slabs. 
Square   Bars  Spaced  Center  to  Center. 


Diameter  of  Rods 


inch 


To 
% 


14275 
16360 
18200 
19800 


3 

ins. 


12350 

14465 
16195 

17745 
19050 
20140 


4 
ins. 


94'5 


13100 

14855 
16330 

17655 


5 
ins. 

7535 
1 1 760 


6280 
9805 


13700 
15205 
16510 
i8755|i77oo 


19740 
20640 


18685 

19595 
20420 


12890 
14360 
15605 
16780 
17830 
18740 
19565 


7 
ins. 

5340 

8330 

12000 


8 
ins. 

4705 

735o 

10590 


9 
ins. 

4170 
6535 
9415 


13540 
1 4880 , 

15995 
17010 

17950 
18800 


1 2995;  12435 
14275 
15345 
16360 

17345 
18200 


10 
ins. 

3765 
5880 

8475 
1 1 535 


ins. 

3420 

5345 
7700 

10475 


12 
ins. 

3HO 
4900 
7060 
9610 


13640113215 
1 4860  j  14330 
15846  15265 
16745116230 
17655117110 


•2745 
13800 
14920 
15790 
16625 


12350 
13420 

14465 
i533o 
16195 


Five-Inch  Concrete   Slabs. 
Round  Rods  Spaced  Center  to  Center. 


Five-Inch   Concrete   Slabs. 
Square  Bars  Spaced  Center  to  Center. 


Diameter  of  Rods 
x/i  inch 

A  "  

H   "  

A  "  

*A    "  

.?_  " 

H   "   ■ 

1 1  " 

T^      

7i     "  


3 

ins. 


17720  14350  10763 


4 

ins. 


8610 

20565  1 7970!  16260  13445 
2294520255  18545  1 7 165 
24900  22270 


5 
ins. 


6 
ins. 


7175 
1 1205 


2651523960 
25460 
26745 


[6030 


7 
ins. 


6100 

9520 

13720 


8 
ins. 


9 
ins. 


5380!  4764 

8400  7470 

12105)10760 


20410  19065. 17855  16935  16145)14650 
2214020755:19605  18585  17720  17090 


10 

ins. 


4305 

6720 

9685 

I3I85 


23675 
25035 
26150 
27225 


22115 

23575 
24805 

25845 


21060,19985  19295 


22425 
23645 


2133020565 
2258021770 


18545 
19815 
21045 


24750  23710:22925  22140 


1 641 5 
18000 
19200 
20315 
21445 


11 

ins. 


3910 
61 10 
8800 

"975 
1 5640 


12 
ins. 

3590 

5600 

8070 

10905 

14350 


17300 
18595 
19755 
20890 


16740 
17990 

19275 
20255 


195 


Five   and  One-half  Inch  Concrete  Slabs. 
Round  Rods  Spaced  Center  to  Center. 


Diameter  of  Rods 


}4  inch 19024 


12680 
23160  19810 
26080  22795 
28575^5260 

3070527385 
3256029380 
3421531055 

•  •  J32540 

•  •  33900 


4 

ins. 


95io 
14850 


20630 
22990 
25120 
27000 

28745 
30255 
31710 


7606 
1 1880 
17110 


6 
ins. 


21285 
23400 

25175 
26875 
28480 
29890 


6340 

9900 

14260 

19400 


7 
ins. 


5390 

8400 

12120 

16500 


21990 

23815 
25420 
26975 
28455 


20680 

22455 
24200 

25635 
27045 


4750 

7425 

10700 

14550 
19000 


9 
ins. 

4230 

6590 

9500 

12940 

17000 


21555 
23160 
24740 
26075  25120 


20630 
22235 
23790 


10 

11 

tns. 

ins. 

3800 

3455 

5940 

5400 

8550 

777o 

1 1 650 

10589 

15210 

13820 

19250 

17500 

21480 
22865 

20705 
22160 

2435o 

23570 

12 
ins. 

3170 

4950 

7125 

9700 

12680 

16050 

1 9810 


1555 
22795 


Diameter  of  Rods 


J4  inch 


To 

li 
9 
Tt5 

% 


Five  and  One-half  Inch  Slabs. 
Square  Bars  Spaced  Center  to  Center. 


21630 
25030 
27800 
30570 
32670 
345oo 


8 

ins. 

16150! 


4 
ins. 


21920 
24810 
27240 
29430 
31300 
32930 
34500 


12110 
18900 


5 

ins. 


9700 
151 10 


22430  20770 
24930123130 
2704525240 
29010  27170 


6 
ins. 


8075 
12600 
18160 


30670 
32150 
33560 


28920 
30400 
31860 


21770 
23760 
25640 
27290 
28970 
30330 


7 
ins. 


6870 
10720 
15430 


20510 
22500 
24470 
26100 
27630 
29060 


6050 

9460 

13620 

18540 


9 
ins. 

536o 

8400 

12110 

16470 


10 
ins. 


21630 
23470 
25030 
26610 
27945 


20680 
22430 
24200 
25635 
27045 


4840 

7560 

10890 

14830 

19390 


ins. 

4390 

6870 

9900 

13360 

17600 


12 
ins. 

4040 

6300 

9080 

12360 

1 6 1 50 


21700 
23350 
24860 
26270 


20920 
22525 
24100 
25420 


20290 
21920 

23425 
24810 


Diameter  of  Rods 


Six-Inch  Concrete  Slabs. 
Round  Rods  Spaced  Center  to  Center. 


inch 21 140 


1  <; 

X 

9 

To" 

% 
1  1 
TS 


2 
ins. 


27540 


3 

ins. 


4 
ins. 


31  no  27240 
34200  30270 
36900,32850 


14100  10570 
22000J 16500 
23760 


39240 
41280 


35220 

37260 

39240 
40830 


5 
ins. 


8450 
13210 
19010 


6 

ins. 


7 
ins. 


599o 

9330 

13470 


27390 
30060 
32340 
3438o 
36360 
38040 


7050 

1 1000 

1 5800 
25290I215201 1 8330 
27750  26190  23940 
3016528300 
32190J30470 
3405032310 
35850J33900 

[196] 


26840 
28860 
30690 
32430 


5275 

8250 

1 1 880 

16150 

21 130 


25590 
27540 
29430 
3H25 


9 
ins. 

4700 
7320 
10550 
14230 
18770 
23770 


10 
ins. 


11 

ins. 


4230  3840 

6600  6000 

9510  8610 

1 29301 1 1750 

16900  15360 

2 1 380  19380 

24000 


12 
ins. 

3520 
5500 
7900 
10760 
14090 
17830 
22000 


2650025485 

28230  27300  26400125560 


30060 


2901027990 


27240 


Six-Inch  Concrete  Slabs. 
Square  Bars  Spaced  Center  to  Center. 


Diameter  of  Rods 


1  1 

:  8 

*4 


H  inch 25650  1 7940 


30000  26040 
335402958026820 


4 
ins. 


5 

ins. 


6 
ins. 


7 
ins. 


8 
ins. 

6720 
10500 
15140 
36690  32640  29800  27540  25830  23350*20600 


13450  10770 
21010  16800 
24200 


89701  7625 
14000  1 1910 

20180  17150 


39330  35280  3243o'3027o;2835o;2688o|25650 


4i55o 


37530  347IO 
36780 
38760 
40380 


39660 
41520 


32560130750 


9 
ins. 


10 
ins. 


595o,  5390 

933oj  8400 

13450  1 2 100 

18300  16480 

23900*2 1 525 


// 
ins. 

4880 

7640 

1 1000 


12 
ins. 

4480 

7o<x> 
10090 


34590 
36540 
38250 


32790 
347io 
36480 


29130^7810 
3144030000 
3306031740 
3480033510 


2682025770 
2883027700 
30690J  29670 
32430^1230 


14840  13730 
19550^7940 
24750  22700 


26900  26040 
2871027780 
3048029580 


To  illustrate  the  use  of  Table  9,  attention  is  called  to  the  following 
example  in  which  the  slab  is  supported  on  two  sides  only: 

Example:  What  size  of  slab  and  what  reinforcement  will  be  neces- 
sary for  the  reinforced  concrete  construction  over  a 
living-room  in  an  all-concrete  house?  It  is  the  intention 
to  reinforce  the  concrete  slab  in  one  direction  only  and 
it  is  considered  that  the  ends  of  the  concrete  slab  are 
fixed.  The  distance  between  the  concrete  beams  is  8 
feet,  and  the  live  or  superimposed  load,  exclusive  of  the 
weight  of  the  construction,  is  70  pounds  per  square  foot. 
The  floor  is  to  be  finished  with  a  wood  floor  secured  to 
sleepers  embedded  in  2  inches  of  cinder  concrete. 

Solution:  The  assumption  is  that  a  4-inch  slab  will  be  sufficiently 
thick,  so  that  the  total  floor  load  per  square  foot  of  slab 
will  be  made  up  as  follows: 

Live  Load 70  (xninds 

Wright  of  Slab 50  pounds 

Weight  of  Flooring 4  pounds 

Weight  of  Cinder  Concrete 15  pounds 

139  pounds  per  square  foot. 

Considering  a  portion  of  the  slab  I  foot  in  width,  the 
total  load  on  such  a  portion  is  equal  to  weight  per  square 
foot  by  the  span  of  the  slab  in  feet,  or 

139  X  8  =  1,112  pounds. 

[197] 


The  bending  moment  of  the  slab  may  be  figured  by  the 

formula 

WL 
10 

or,  if  the  span  is  taken  in  feet  and  the  result  is  desired  in 

inch-pounds: 

M  =  i.2  WL. 

If  the  weight  W=  1,112  pounds,  and  the  span  in  feet,  or 

L  =  8,  then  by  substitution 

M  =  1.2  X  1,112  X  8  =  10,675  inch-pounds. 

Assuming  that  it  is  desired  to  use  square  twisted  bars, 

refer  to  the  portion  of  Table  9  relating  to  4-inch  slabs. 

It  will  be  seen  that  ^8_mcn  square  bars,  spaced  5  inches 

from    center    to    center,    have   a    resistance    of    10,650 

inch-pounds,    which    is    sufficiently    close    for    practical 

purposes. 

In  order  to  illustrate  further  the  use  of  Table  9,  the  following  prob- 
lem in  the  design  of  a  rectangular  slab  supported  on  all  four  sides  is 
given : 

Example:  A  floor  slab  in  a  dwelling-house  is  supported  on  all  four 
sides  by  outside  and  partition  walls.  The  length  of  the 
slab  is  14  feet,  and  the  width  is  10  feet,  while  the  total 
load,  including  the  weight  of  the  slab,  is  120  pounds  per 
square  foot.  Determine  the  thickness  and  the  reinforce- 
ment necessary  for  reinforcing  the  slab  in  both  directions. 

Solution:  It  is  first  necessary  to  find  the  ratio  of  the  length  of  the 
slab  to  the  breadth  (as  explained  on  page  185).  This 
ratio,  or 

T     _M,  or  1.4; 
Lp_io 

then,   from  Table  8,  the  proportion  of  the  load  carried 

by  the  short  and  the  long  span  is  found  for   the  value 

of  1.4  to  be  .79  and  .21  respectively.    The  load  in  pounds, 

therefore,  to  be  carried  by  the  short  span  would  be 

.79  X  120  =  94.80  pounds  per  sq.  foot, 

while  for  the  long  span  the  weight  producing  the  bending 
moment  would  equal 

.21  X  120  =  25.20  pounds  per  sq.  foot; 
[198] 


the  next  thing  to  find  is  the  proportionate  weight  on  the 
slab  both  ways  for  a  strip  of  slab  i  foot  in  width,  and 
these  weights  are  as  follows: 

Wb=K>  X  94.80  =  948  pounds. 
Wi  =  i4  X  25.20  =  353  pounds; 

as  the  span  and  load  are  taken  from  center  to  center  of 
supports  the  bending  moment  both  the  short  way  and 
the  long  way  of  the  slab  is  then  calculated  by  the  formula 

™    WL 

M=  ,o' 

or,  using  L  in  feet,  and  obtaining  the  results  in  inch- 
pounds, 

M  =  i.2  WL. 

This  calculation  is  as  follows: 

Bending  Moment 

Short  Way  of  Slab  =1.2  X    948  X  10=11,376 
in.  lbs. 
Bending  Moment 

Long   Way   of  Slab=l.2   X   352   X    14  =  5,914 
in.  lbs. 

Table  9  may  now  be  used  for  determining  what  slab  and 
what  reinforcement  will  be  necessary  to  give  the  required 
resistance. 

Note. — It  is  best  in  making  selections  from  the  table,  where  rectan- 
gular slabs  are  concerned,  to  use  first  the  bending  moment  short  way  of 
the  slab. 

In  above  example  the  bending  moment  the  short  way  of 
the  slab  is  11,376  inch-pounds.  Referring  to  Table  9 
it  will  be  observed  that  a  41/£-inch  slab,  reinforced  with 
%-inch  square  twisted  bars  placed  7  inches  from  center 
to  center,  has  a  resistance  of  12,000  inch-pounds,  and  that 
if  J^-inch  square  twisted  bars  spaced  6  inches  on  centers 
arc  used  the  long  way  of  the  slab,  the  resistance  will  be 
6,280  inch-pounds,  which  is  in  excess  of  the  bending 
moment  of  5,913  inch-pounds  created  in  the  slab  length- 
wise. 

[  199] 


Resisting  Moments  of  Rectangular  Beams. — While  the  resist- 
ing moment  of  rectangular  reinforced  concrete  beams  may  be  found 
with  little  trouble  when  the  percentage  of  the  steel  reinforcement  and 
the  location  of  the  neutral  axis  have  been  found,  nevertheless  when  the 
bending  moment  has  to  be  calculated  it  is  much  more  convenient  to 
determine  the  actual  size  and  reinforcement  needed  directly  from  a 
table  giving  resisting  moments  for  rectangular  beams  of  different  depths 
and  reinforced  with  different  percentages  of  steel  reinforcement.  Con- 
sequently, the  resisting  moments  in  inch-pounds  are  given  in  Table  10. 
The  values  in  this  table  are  limited  by  an  allowable  unit  fiber  stress  on 
the  steel  of  16,000  pounds,  and  an  allowable  unit  compressive  stress  on 
the  concrete  at  the  extreme  edge  of  600  pounds,  and  a  ratio  of  12. 

Referring  to  the  table  it  will  be  observed  that  the  resisting  moments 
are  given  for  beams  reinforced  with  T%  of  one  percent  to  1  percent  of 
steel,  varying  by  one-tenth  of  one  percent,  and  also  for  beams  from 
6  inches  to  36^  inches  in  depth.  The  large  values  in  the  columns  are 
the  resisting  moments  in  inch-pounds  for  each  inch  in  width  of  the  beam, 
while  the  decimal  values  are  the  areas  of  the  steel  reinforcement  required 
in  square  inches  for  each  inch  in  width  of  the  beam.  It  will  also  be 
noticed  from  the  figure  accompanying  the  table  that  the  depth,  or  the 
distance  d  given  in  the  column  to  the  extreme  left,  is  the  distance  from  the 
center  of  action  of  the  steel  to  the  top  of  the  beam,  and  is  not  the  total 
depth  of  the  beam. 

The  following  example  illustrates  the  use  of  the  above  table: 

Example:  A  rectangular  reinforced  concrete  beam  supported  on  the 
columns  of  a  portico,  supports  a  tile  roof  which  imposes 
a  total  load  of  500  pounds  per  running  foot;  the  span  of 
the  beam  is  20  feet.  Determine  the  size  of  the  beam 
and  the  amount  of  reinforcement  necessary  to  carry  the 
weight. 

Solution:  The  total  load  on  the  beam  is  20  X  250,  or  5,000  pounds, 
and  as  the  beams  are  not  fastened  at  the  ends,  the  bend- 
ing moment  in  inch-pounds  is  found  by  the  formula 

M=  I  ,  or,  ii  WL. 


TABLE  10.— RESISTING  MOMENTS  IN   INCH-FOUNDS  OF  RECTANGULAR 
REINFORCED  CONCRETE  BEAMS.     (Per  Inch  in  Width  of  Beam.) 

Ratio  of  Steel  Reinforcement. 


d    i 


.005 


5219 
585' 
6520 
7224 


6  I  2601 

634  3052 

7  I  3540 
7K>  4o64 

4623 

9 

9lA 

10 

io}4  7965 

11  8741 

hMj  9554 

12  10403 
12^11288 

13  1 12209 
I334i3i66 

14  !4i59 

14K15189 

15  16254 
15^17355 

16  18493 

1 6  >2  19667 

17  20877 

I7^'22I24 

18  J 23406 
18^24724 
I Q      26079 

193327469 
20  I28896 
20,1^30359 

21  31758 

21 34  33493 

22  34964 
22^36572 

23  38215 
23^  39895 

24  41610 
24^43362 

25  45i5o 
25M46974 

26  48834 
26 34  50731 

27  52663 

27  H  54632 

28  56636 
28^  58677 

29  60754 
293^62867 

30  65016 

30  y2  67201 

31  69423 
31^  71680 

32  73974 
32^76314 

33  78669 
33^81071 

34  83509 
343485984 

35  88494 
35H91040 

36  93623 
36  y2  96243 


.006 

.007 

.008 

030 

3036 

036 

3214 

.042 

3365 

.048 

033 

3563 

039 

3772 

.046 

3949 

.052 

035 

4132 

.042 

4374 

.049 

458o 

.056 

038 

4743 

045 

5022 

.052 

5257 

.060 

040 

5397 

048 

57H 

.056 

5982 

.064 

043 

6093 

.051 

6450 

.060 

6753 

.068 

045 

6831 

054 

7231 

.063 

7571 

.072 

048 

761 1 

057 

8057 

.067 

8435 

.076 

050 

8433 

060 

8927 

.070 

9347 

.080 

053 

9298 

•063 

9842 

.074 

10305 

.084 

055 

10104 

.066 

10802 

.077 

1 1 309 

.088 

058 

1 1 153 

.069 

1 1 806 

.081 

1 236 1 

.092 

060 

12144 

.072 

12855 

.084 

13459 

.096 

063 

I3I77 

•075 

13949 

.088 

14604 

.100 

065 

14252 

.078 

15087 

.091 

15796 

.104 

068 

i537o 

.081 

16270 

•095 

17034 

.108 

070 

16530 

.084 

17498 

.098 

18319 

.112 

073 

17732 

.087 

18780 

.102 

1 965 1 

.116 

075 

18976 

.090 

20087 

.105 

21032 

.120 

078 

20262 

•093 

21448 

.109 

22455 

.124 

080 

2 1 590 

.096 

22854 

.112 

24127 

.128 

083 

22960 

.099 

24305 

.116 

25446 

•132 

085 

24373 

.102 

25800 

.119 

2701 1 

.136 

088 

25828 

.105 

27340 

.123 

28624 

.140 

090 

27325 

.108 

28925 

.126 

30283 

.144 

093 

28864 

.111 

30554 

.130 

31988 

.148 

095 

30445 

.114 

32228 

•  133 

33741 

•C52 

098 

32069 

.117 

33946 

.138 

35540 

.156 

IOO 

33740 

.120 

357io 

.140 

37386 

.160 

103 

35443 

.123 

37517 

.144 

39279 

.164 

I05 

37193 

.126 

39370 

•147 

41218 

.168 

I08 

38985 

.129 

41267 

.151 

43204 

.172 

no 

40819 

.132 

43209 

•154 

45237 

.176 

113 

42696 

•135 

45195 

.158 

47317 

.180 

115 

44614 

.138 

47226 

.161 

49443 

.184 

Il8 

46575 

.141 

49302 

.165 

51616 

.188 

I20 

48578 

.144 

51422 

.168 

53836 

.192 

123 

50623 

•147 

53587 

.172 

56102 

.196 

125 

5271 1 

.150 

55796 

•175 

58416 

.200 

128 

54840 

•153 

58050 

.179 

60777 

.204 

I30 

5701 1 

.156 

60349 

.182 

63182 

.208 

133 

59226 

•159 

62693 

.186 

65636 

.212 

135 

61482 

.162 

65081 

.189 

68136 

.216 

138 

63779 

.165 

67513 

•  193 

70683 

.220 

I40 

66120 

.168 

69990 

.196 

73277 

.224 

143 

68503 

.171 

72513 

.200 

75917 

.228 

145 

70928 

.174 

75079 

.203 

78604 

■232 

I48 

73395 

•177 

77691 

.207 

81338 

•236 

I50 

75903 

.180 

80347 

.210 

841 19 

.240 

153 

78454 

.183 

83047 

•214 

86946 

.244 

155 

81048 

.186 

85792 

.217 

89820 

.248 

158 

83683 

.189 

88582 

.221 

92740 

■252 

I60 

86361 

.192 

91418 

.224 

957o8 

•  256 

163 

89081 

•  195 

94296 

.228 

98722 

.260 

165 

91843 

.198 

97220 

.231 

101783 

.264 

168 

94647 

.201 

100188 

•235 

I 0489 1 

.268 

I70 

97494 

.204 

103200 

.238 

108046 

.272 

173 

100382 

.207 

106258 

.241 

1 1 1247 

.276 

175 

103313 

.210 

109360 

•245 

1 14495 

.280 

178 

106286 

•213 

1 12508 

.249 

1 1 7790 

.284 

l8o 

109300 

.216 

1 15700 

.252 

121130 

.288 

183 

1 12362 

.219 

1 1 8930 

.256 

124513 

.292 

.009 

3505 
4102 

4757 
546i 
6213 
7014 
7864 
8762 
9708 
10704 

1 1 747 
12839 
13980 
15169 
16407 
17694 
19028 
20412 
21844 
23324 
24854 
26431 
28057 
29732 
3H55 
33227 
35047 
36916 

38834 
40800 
42814 

44877 
46989 
49149 
51357 
53615 
561 15 
58275 
60678 
63129 
65639 
68177 
70774 
73420 
761 14 
78856 
81648 
84487 
87376 
90312 
93299 
96332 
99414 

102545 
105724 
108953 
1 12229 

"5554 
1 18928 
1 22350 
1 2582 1 
129335 


.01 

•054 

3616  . 

059 

4244  . 

063 

4922  . 

068 

5651  • 

072 

6429  . 

077 

7258  • 

081 

8i37  • 

086 

9066  . 

090 

10045  . 

095 

1 1075  . 

099 

12155  • 

104 

13285  • 

108 

14465  • 

113 

15696  . 

117 

16978  . 

122 

18308  . 

126 

19689  . 

131 

21 120  . 

135 

22602  . 

140 

24134  • 

.144 

25716  . 

.149 

27349  • 

•153 

29031  . 

.158 

30764  • 

.162 

32547  ■ 

.167 

3438o  . 

.171 

36264  . 

.176 

38198  . 

.ISO 

40182  . 

.185 

42216  . 

.189 

44300  . 

.194 

46435  • 

.198 

48620  . 

.203 

50855  • 

.207 

53140  . 

.212 

55476  . 

.216 

57862  . 

.221 

60298  . 

.225 

62784  . 

.230 

65320  . 

•234 

67907  • 

•239 

70544  • 

•243 

73232  . 

.248 

75968  . 

•252 

78756  . 

•257 

81594  • 

.261 

84482  . 

.266 

87420  . 

.270 

90409  . 

•275 

93447  • 

.279 

96536  . 

.284 

99676  . 

.288 

102865  . 

•293 

106105  . 

.297 

109394  • 

.302 

"2735  • 

.306 

116125  . 

•3" 

1 19565  • 

•315 

123056  . 

.320 

126597  . 

324 

130188  . 

329 

133825  • 

060 
065 

070 

075 
080 
085 

090 

095 

IOO 

105 

no 

"5 
120 

125 

130 
135 

140 

145 

>5o 
155 
160 

165 
170 

175 
180 

185 
190 

•95 
200 
205 
210 

215 
220 
225 
230 
235 
240 

245 
250 

255 
260 
265 
270 

75 
280 

285 
290 
295 
3°o 
305 
310 

315 
320 

325 
330 
■335 
340 
345 
350 
355 
t,6o 

365 


so  that  by  substitution 

M  =  i|  X  5,ooo  X  20  =  150,000  inch-pounds. 

The  width  of  rectangular  beams  is  generally  determined 
either  by  an  architectural  or  structural  requirement. 
The  minimum  width  of  beams  on  account  of  practicability 
of  construction  is  usually  6  inches,  and  in  house  construc- 
tion the  maximum  width  would  seldom  exceed  12  inches. 
Assume  that  a  beam  10  inches  in  width  is  to  be  used,  the 
resistance  for  each  inch  in  width  would  equal 

150,000^-  10,  or  15,000  inch-pounds; 

referring  to  Table  10,  the  column  headed  ".006,"  it  will 
be  seen  that  a  beam  from  13V2  inches  to  14  inches  in 
depth  will  answer,  and  that  the  total  area  of  steel 
reinforcement  will  equal 

.081   X  10  =.8 1  square  inch. 

Therefore  two  ^g-inch  square  twisted  bars  will  be  nearly 
enough,  and  two  %-inch  much  more  than  is  required  for 
reinforcing  the  beam. 

If  the  beam  is  designed  as  a  rectangular  section  supporting  the  floor 
slab,  the  depth  of  the  beam  is  considered  from  the  top  of  the  slab  to  the 
center  of  reinforcing  in  the  beam.  This  must  leave  at  least  1^/2  inches  of 
concrete  under  the  steel,  to  act  as  fireproofing. 


[  202  ] 


Chapter  VIII 
Concrete  Block  Houses 


*•   o 
to  £ 


Chapter  VIII 
Concrete  Block  Houses 

The  demand  for  better  homes,  for  more  sanitary,  permanent  and  fireproof 
houses  of  moderate  cost,  led  to  the  enthusiastic  reception  accorded  the 
concrete  building  block.  In  skilled,  intelligent  hands,  many  remarkably 
beautiful  and  satisfactory  dwellings  have  been  and  are  being  built  of 
this  cement  product.  On  the  other  hand,  especially  in  the  earlier  days 
of  the  industry,  not  a  few  unsightly  and  unsatisfactory  structures  re- 
sulted. The  fact  that  little  or  nothing  is  said  of  success,  while  great 
publicity  is  given  to  failure,  has  led  many  to  believe  that  good  houses 
cannot  be  built  of  concrete  blocks.  Such  is  far  from  the  case:  many  of 
the  best  architects  in  the  country  have  designed  and  built  residences  of 
concrete  blocks,  some  of  which  have  cost  more  than  one  hundred  thousand 
dollars.  From  the  smallest  cottage  to  the  palatial  mansion,  these  struc- 
tures are  satisfactory  in  every  detail — the  combination  of  tasteful  design 
with  good  workmanship. 

Designing  the  Block. — With  regard  to  the  size  and  proportional 
dimensions  of  the  block  or  blocks,  little  can  be  said  other  than  that  these 
details  should  be  in  perfect  keeping  with  the  general  architectural  style 
of  the  structure.  The  same  holds  true  in  the  matter  of  surface  finish 
of  the  block.  Concrete,  as  concrete,  has  sufficient  beauty  in  itself  to 
make  imitation  of  other  materials  not  only  unnecessary,  but  even  repre- 
hensible. Too  frequently  mechanics  have  designed  and  marketed  block 
molds  perfect  mechanically  but  so  bad  esthetically  that  architects  have 
often  rightfully  refused  to  use  the  product.  With  a  simple  mold  of  plain 
design,  an  artisan  can  produce  a  block  of  wonderful  beauty  and  utility. 
To  bring  out  the  beauty  of  the  concrete,  the  exterior  of  the  block  is 

[205] 


finished  in  accordance  with  any  of  the  several  methods  given   under 
"Surface  Treatment,"  page  122. 

Making  the  Block. — The  selection,  proportioning  and  mixing  of 
the  aggregate  for  concrete  blocks  are  governed  in  general  by  the  informa- 
tion covering  these  subjects  on  preceding  pages.  On  account  of  the 
narrowness  of  the  spaces  of  molds,  the  maximum  size  of  stone  permissible 
in  a  well-graded  aggregate  is  usually  Y2  to  %  mcn  m  diameter.  The 
Portland  cement,  sand  and  crushed  rock  should  be  combined  in  such 
proportions  as  to  form  a  dense,  damp-proof  block.  This  correct  pro- 
portion is  determined  by  methods  previously  described.  For  average 
conditions,  with  sand  grading  uniformly  from  o  to  34  mcn  and  stone  from 
Y%  to  Yi  inch,  the  concrete  is  generally  proportioned  1  part  cement  to 
1 V2  parts  sand  to  3  parts  crushed  rock  or  1  part  cement  to  2  parts  sand 
to  4  parts  crushed  rock.  With  clean,  well-graded,  crusher-run  stone 
screenings  or  bank-run  gravel,  the  proportions  are  most  frequently  I  to  3 
or  1  to  4.  When  sand  alone  is  used,  more  cement  is  required.  Such 
concrete  is  most  often  proportioned  I  to  2  or  I  to  3.  In  order  to  produce 
blocks  similar  in  quality  and  appearance,  all  materials,  including  the 
water,  should  be  accurately  measured  by  volume. 

It  is  highly  important  that  an  abundance  of  water  be  used  in  the 
concrete  for  blocks.  The  cement  requires  it,  and  in  no  other  way  can 
dense,  damp-proof  blocks  be  made.  The  quantity  of  water  necessary 
to  a  given  amount  of  dry  materials  varies.  If  the  block  is  made  by  tamp- 
ing, there  should  be  at  least  sufficient  water  that  liquid  cement  will  flush 
to  the  surface  when  the  concrete  is  rammed  into  the  block  mold.  Fre- 
quently block  manufacturers,  in  their  efforts  to  turn  out  quantities  of 
blocks  with  a  minimum  number  of  molds,  have  made  the  very  serious 
mistake  of  mixing  the  concrete  too  dry,  so  that  the  blocks  might  be 
stripped  of  the  molds  more  quickly.  No  amount  of  tamping  will  pro- 
duce density  in  a  concrete  lacking  sufficient  water.  Concrete  for  poured 
blocks  is  usually  of  the  consistency  known  as  "mushy"  or  "quaking." 

Curing   Cement    Products. — To    cure    concrete    products    rapidly 

[206] 


ft  t 
■h  -= 


in 

o 

-/ 

X 

- 

o 

— 

■ , 

■— 

u 

w 

o 

>* 

•= 

c 

u 

L 

hfi 

O.K 

u 

C 

rt 

■- 

"O 

2  c 


0  -5 


3 -as 

a  E  g 


ft  2 


^  IS 


-«    rt  bo 

S     60  C 

*    o   o 

s  bo  c 

•■a  «)  rt 

a  "C  x 

IP  (j  « 

*■*"     -w    O 
,      u  45 

?  8-g 

°  is— 

o  "rt 
a  a. 


o  .B 


and  with  the  best  results,  heat  and  moisture  are  essential.  A  thorough 
understanding  and  practice  of  these  requirements  enable  the  manu- 
facturer not  only  to  market  his  product  sooner,  but  also  to  produce  a 
superior  article. 

Sufficient  water  must  be  incorporated  with  the  concrete  previous 
to  molding  and  must  be  conserved  in  the  product  until  it  is  thoroughly 
cured.  After  the  block  is  molded,  precautions  must  be  taken  to  protect 
it  from  sun,  wind  and  frost  until  the  cement  has  thoroughly  set.  (See 
instructions  for  protection  of  freshly  placed  concrete,  page  1 17.)  Open- 
ings to  the  curing  room  are  closed  by  doors  or  canvas,  so  as  to  cut  off 
all  drafts,  which  tend  to  remove  moisture  from  the  concrete  product. 
Moreover,  as  soon  as  possible  without  pitting  the  surface,  the  freshly 
molded  units  are  sprinkled  with  water  and  the  operation  repeated 
at  intervals  of  four  to  twenty-four  hours  for  five  to  seven  days. 
When  seven  days  old,  blocks  may  be  piled  in  the  open  air.  Even  then 
an  occasional  wetting  is  beneficial.  Ordinarily  cured  blocks  should  not 
be  placed  in  the  wall  until  they  have  attained  the  age  of  at  least  thirty 
days,  as  freshly  made  concrete  contracts  slightly  until  the  cement  has 
attained  its  full  set,  and  small  shrinkage  cracks  might  appear  at  the 
mortar  joints. 

Portland  cement  sets  up  more  quickly  in  warm  weather  than  in 
cold.  Within  recent  years  many  cement  products  manufacturers  have 
been  taking  advantage  of  this  characteristic  of  cement  by  installing 
steam-curing  plants.  With  steam  even  at  atmospheric  pressure,  it 
has  been  found  that  in  a  steam-tight  kiln  the  concrete  becomes  suffici- 
ently hard  in  the  course  of  a  few  days  to  permit  the  shipping  of  the 
product. 

£>  Exhaustive  tests  made  by  the  United  States  Bureau  of  Standards 
have  deduced  the  fact  that  a  compressive  strength  of  concrete  consider- 
ably in  excess  of  that  obtained  normally  after  aging  for  six  months  can 
be  obtained  in  two  days  by  subjecting  the  product  to  steam  under 
considerable  pressure.  Moreover,  steam-cured  products  are  lighter  in 
color  and  much  more  uniform  in  appearance  than  concrete  of  the  same 
aggregate  cured  by  ordinary  methods. 
14  [209I 


Advantage  of  Block  Construction. — The  concrete  block  is  the 
simplest  form  of  unit  construction.  Since  it  is  a  factory  product,  the 
same  mold  is  used  many  times  for  many  different  structures,  with  a 
resulting  small  charge  for  forms.  Each  unit  can  be  carefully  inspected 
for  quality  and  uniformity  of  appeal  ance  previous  to  erection  in  the  house 
wall  and  all  faulty  pieces  rejected.  A  concrete  block  house  presents  no 
unusual  difficulties  of  construction.  Masons  of  ordinary  skill  can  build 
a  residence  with  concrete  blocks  much  more  quickly  and  cheaply  than 
with  ordinary  stone  or  brick.  The  floors  and  interior  finish  are  the  same 
as  those  usually  given  masonry  structures. 

The  architect  interested  in  concrete  blocks  may  obtain  them  from 
manufacturers  who  make  a  standard  pattern,  or,  if  these  are  not  satis- 
factory, he  may  select  his  own  aggregates  and  surface  finish,  even  to  the 
extent  of  having  special  face  molds  made  for  machines  used  in  the  manu- 
facture of  ordinary  blocks.  This  was  done  in  the  case  of  the  Steers' 
residence,  shown  on  another  page.  This  large  and  costly  dwelling  was 
built  of  blocks  cast  in  plain  form  on  a  machine  of  simple  pattern,  but  with 
aggregates  selected  and  mixed  to  give  the  required  color  and  texture. 
This  dwelling  is  an  excellent  example  of  the  utility  of  the  concrete  block 
when  in  competent  hands,  as  it  represents  the  combined  efforts  of  prom- 
inent architects  and  engineers. 

Where  the  architect  selects  the  block  made  by  the  manufacturer, 
he  should  make  certain  that  it  is  of  the  very  best  quality  as  to  density 
and  strength.  In  the  matter  of  porosity,  however,  it  may  be  said  that 
blocks  which  admit  moisture  when  first  erected  sometimes  become 
thoroughly  water  tight. 

The  concrete  block  is  especially  valuable  in  localities  scarce  in  timber, 
where  the  cost  of  forms  for  poured  or  cast  houses  might  be  excessive. 
In  some  countries  the  block  has  taken  piecedence  over  reinforced  con- 
crete for  house  wall  construction,  notably  in  England,  Scotland  and  Ire- 
land. These  countries  have  surpassed  the  United  States  in  attractive 
block  buildings,  especially  of  the  cottage  type.  They  are  usually  con- 
structed of  the  severely  plain  block,  such  as  is  shown  in  the  accompanying 
illustrations.     There  has  been  no  attempt  at  fantastic  shapes  or  orna- 

[210] 


mentation,  merely  the  substitution  of  the  concrete  block  for  plain, 
dressed  stone. 

The  several  illustrations  of  block  houses  show  the  attractive  char- 
acter of  the  material  when  used  in  the  most  direct  and  unpretentious 
manner. 

The  design  of  reinforced  concrete  buildings  requires  an  understand- 
ing of  at  least  such  elementary  principles  of  engineering  as  will  insure 
safety  to  the  structure,  but  with  blocks  the  builder  may,  generally  speaking, 
proceed  as  with  brick  or  stone.  As  is  the  case  with  all  materials  used 
in  unit  construction,  however,  each  requires  special  treatment,  but  the 
laying  up  of  a  block  wall  is  not  more  difficult  or  complicated  than  the 
construction  of  a  wall  of  brick  or  stone.  In  brief,  the  block  is  an  excellent 
substitute  for  these  materials,  whether  applied  to  dwellings  or  buildings 
of  larger  size. 


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Administration  Building,  Washington  Park,  Chicago. 

An  especially  interesting  example  of  untreated  surface. 
(See  pages  123  and  124.) 


Alphabetical   List  of  Architects,  Engineers  and 

Builders    Whose    Work    is    Represented    in    the 

Illustrations  Contained  in  this  Book* 


ARCHITECTS 

PAGE 

Atterbury,  Grosvenor,  New  York 10,  84 

Beatty,  C.  N.,  Hot  Springs,  Ark 176 

Blake  &  Butler,  New  York 208 

Buchanan,  C.  W.,  Pasadena,  Cal 35 

Carrere  &  Hastings,  New  York 208 

Chapman  &  Frazer,  Boston 13 

Clark,  C.  C,  Akadena,  Cal 169 

Covell,  William  S.,  New  York 170 

Elzner  &  Anderson,  Cincinnati 25 

Fernekes  &  Cramer,  Milwaukee 22,  23,  64 

Kahn,  Albert,  Detroit  (Frontispiece) 71 

Lord  &  Hewlett,  New  York 207 

McKean,  R.  W.,  Riverside,  Cal 190 

McKim,  Mead  &  White,  New  York 7 

Parrish,  W.  H.,  Carnegie,  Pa 120,  181,  182 

Parry,  Oliver  Randolph,  Philadelphia 35,  218 

Plack,  W.  L.,  Philadelphia 25 

Purdon,  James,  Boston 33 

Putnam  &  Cox,  Boston 78 

Read  &  Morrill,  Brooklyn 109 

Richards,  H.  H.,  Chicago 204 

Rocking,  F.  L.,  Pasadena,  Cal 32 

Rotier,  H.  J.,  Milwaukee 212 

Shaw,  Howard  V.,  Chicago 132,  21 1 

Simon,  Grant  M.,  Philadelphia 14,  145,  153,  154 

Smith,  John  J.,  Winthrop,  Mass 27 

Thome,  Harry  E.,  Ottumwa,  Iowa no 

Tracy  &  Swartout,  New  York 131,  161 

Warren  &  Wetmore,  New  York 162 

Wilby,  Ernest,  Detroit Frontispiece 

ENGINEERS 

Aberthaw  Construction    Company,   Boston 119 

Howes,  Benjamin  A.,  New  York 48,49,50,51,  125,  138,  170,214,215 

Simpson  Bros.,  Boston 220 

Turner  Construction  Co.,  New  York 162 

Bl'ILDERS 

Bosworth,  P.  H.,  San  Francisco 18,  135 

Carey  &  Reed,  Philadelphia 14,  72,  87,  145,  153.  154 

Knapp,  C.  R.,  Albany 77 

Riley,  W.  H.,  Riverside,  Cal 188 

*  In  a  few  cases  it  was  impossible  to  obtain  names  of  architects  and 
omissions  were,  therefore,  unavoidable. 

[217] 


Church  Window,  Lynn,  Mass.  Simpson  Bros.,  Engineers,  Boston 

Architectural  detail  cast  in  concrete.     Equals  stone  in  strength  and  appearance 

and  costs  much  less. 


Ind 


ex 


Ind 


ex 


Abrased  and  tooled  surfaces,  124 

Adaptability  of  concrete,  6 

Advantages  of  concrete  for  house  con- 
struction, II 

Aggregates,  85,  86,  89,  129 

Architectural  composition,  23 

Architectural  decoration  in  color,  42 

Architectural  design  and  treatment,  19 

Architectural  details  of  molded  and  cast 
concrete,  40 

Architectural  details  of  monolithic  con- 
struction, 34 

Artificial  colors,  133 


Bars — plain,    corrugated    and    deformed, 

58,  59 
Beams  and  girders,  148,  178 
Beams  and  slabs  (illustration),  55 
Bending  moments,  177,  184 
Bending  reinforcement,  115 
Blocks,  205 

Blocks,  advantage  of,  210 
Blocks,  curing  of,  206 
Blocks,  design  and   manufacture  of,  205, 

206 
Brushing  surfaces,  125 
Built-up  form  construction,  94 
Buttress  construction  (illustration),  23 


Calculating  bending  moments,  177  to  187 

inclusive 
Calculations  for  reinforced  concrete,   139 

to  171  inclusive 
Centering,  93 

Cinder  concrete,  67,  86,  89 
Collapsible  forms,  96 
Colonial  types  (illustration),  33 
Color  decoration,  42 
Colored  surfaces,  133,  134 
Columns,  78,  167,  168 
Concrete  blocks,  205 
Concrete  in  compression,  159,  164 
Concrete  copings,  66 


Concrete  form  separator,  102 
Concrete  residence  of   costly  type    (fron- 
tispiece) 
Concrete  and  rubble  work  (illustration),  35 
Concrete  wall  construction,  75,  76 
Conductivity,  resistance  to,  15 
Conflagration  test  of  concrete,  26 
Consistency  in  design  (illustration),  28 
Constructive  forms,  96 
Copings,  66 

Cored  slabs  (illustration),  84 
Core  tile  construction,  97 
Cost  of  steel  for  reinforcing,  113 
Country  houses,  33 
"Curry  Tyer, "  118 


inlay    (illustra- 


41 
construe- 


Dead  loads,  171 
Decoration  in  color,  42 
Decoration    with    mosaic 

tion),  45,  131,  161 
Decoration  with  tile  inlay,  42 
Decorative  details  (illustration) 
Decorative   features  of   timber 

tion,  44 
Density  of  concrete,  89 
Designing  reinforcement,  191 
Details  of  construction,  55 
Development  of  particular  style,  19 
Displayed  selected  aggregates,  129 
Door  frames,  70,  74,  75 
Doorways  (illustrations),  36,  37,  45,  54,  71 
Double  reinforcement,  185 
Dry  mixed  concrete,  91 
Durability,  12,  70 


Earthquake,  resistance    to     (illustration), 

13 
Eaves,  68,  69,  70 
Elaboration  of  design,  39 
Entablatures,  40 

Estimates,  a  practical  example,  93 
Estimating  quantities  of  materials,  92 

l] 


Expanded  metal,  59,  114 
Expansion  joints,  66,  67 
Exterior  finish  (illustration),  88 
Exterior  surface  decoration  (illustration). 
18 


Fabricated  reinforcement,  50,  60 

Fabricating  reinforcement,  115 

Facade  design,  proper  treatment  of  (illus- 
tration), 39 

False  treatment  (illustration),  20 

False  work,  93 

Felt  roof  coverings,  65,  66 

Ferro-Dome  construction,  97 

Ferro-Inclave,  67 

Fire  losses,  5 

Fireplaces  (illustrations),  48,  49,  50,  145 

Fireproof  qualities,  1 1 

Flashing,  66,  68,  69 

Flat  roofs,  62,  65 

Floor  construction,  55,  61,  76 

Floor  covering  of  wood,  62 

Floor  finish,  61 

Floor  loads,  174 

Floors  of  terra  cotta  tile,  56,  57 

Flower  boxes  (illustration),  72 

Form  holders,  104 

Forms,  77,  78,  94  to  1 1 1  inclusive 

Forms  for  one-story  stages,  98 

Forms  for  wall  construction,  97 

Form  work  and  centering,  93 

Fountain,  72 

Frank  treatment  of  concrete  (illustration), 
14,  22,  73,  87,  153,  154 

Frieze,  44 

Furred  walls,  81 


Girders,  55 

Glue  molds,  use  of  in  intricate  design,  39 

Gravel,  86,  89 

Gutter  construction,  68,  69,  70 


Half-timber  design   (illustrations),  25,  46 

Hand  mixing,  90 

Heating  materials  in  cold  weather,  121 

Hinton  floor  system,  57 

Hollow  concrete  walls,  80,  105 

Hook  bolts  for  forms,  101 


Interior  construction  (illustrations),  7,  72 
Interior  decoration  and  details,  44,  48,  52 
Interior  treatment   (illustrations),  48,  49, 
50,  51 


Joining  frame  and  wall  construction,  73 

Joints,  66 

Joists,  55,  78,  79 

Joists,  methods  of  supporting,  78,  79 


Kahn  bar,  59 


Lever  arm  determination,  150 

Lined  walls,  81 

Live  and  dead  loads,  171 

Loads,  168,  171,  172,  173,  174 

Long  span  construction  (illustrations),  27, 

30 
Low  cost  of  up-kecp,  16 


Machine  mixing,  89 

Mantels  (illustrations),  49,  50 

Materials,  85,  86,  92 

Measuring  boxes,  90 

Measuring  ingredients,  89,  90 

Metal  lath,  67 

Method  of  supporting  floors,  76 

Methods  and  types  of  steel  reinforcement, 
58 

Methods  of  finishing  floors,  61 

Mission  style  (illustration),  32 

Mixing,  86,  89,  90,  91 

Modulus  of  elasticity,  149 

Molded  and  cast  details,  40 

Monolithic  concrete,  architectural  details 
of,  34 

Monolithic  construction  expressed  in  de- 
sign (illustration),  29 

Mortar  facings,  123 

Mosaic  decoration,  134 

Mosaic  inlay  for  surface  decoration 
(illustration),  45 

Mushroom  system,  57 


Neutral   axis,    formulas   for   determining. 

149 
Non-conductivity,  15,  75 


Operations  in  the  field,  85 

Ornamental  details  (illustrations),  41,  54 

Ornament  expressed  in  color,  42 

Ornamental  mosaic    (illustration),   45 

Ornament,  precast,  44 

Ornamental  tile,  42 


Paneling  in  concrete,  44 

Panel  or  sectional  wall  form,  103 

Pedestal  of  concrete  (illustration),  43 

[  222  ] 


Placing  reinforcement,  115 

Porch  construction  (illustrations),  23,  27, 

29.  30,  31.  35.  40.  47.  72,  87,  153,  154 
Portland  cement,  85 
Posts,  167 

Pouring  concrete,  78 
Precast  concrete  construction,  84 
Precast  detail  (illustrations),  41,  42,  43 
Primary  and  secondary  reinforcement,  142 
Principles  of  reinforced  concrete,  139 
Profiles  suitable  for  detail  (illustration),  38 
Projecting  masonry  (illustration),  25 
Proportioning  and  mixing,  86,  89 
Protection  of  work,  117,  121 
Reinforcing  bars,  58,  59,  60,  61,  III,  112 
Reinforcing,  calculations  for,   177  to  199 

inclusive 
Reinforcing  steel,  kinds  of,  112 
Reinforcing  stirrups,  59,  61 
Reinforcement,  139  to  171  inclusive 
Reinforcement  of  joists,  55 
Reinforcement  of  roofs,  67 
Repairs,  avoidance  of,  16,  70 
Residence  in  Jamaica  (illustration),  13 
Resisting  moment,  151,  155,  200,  201,  202 
Roof  construction,  62,  65,  66,  67,  68,  69, 

70 
Roof  coverings,  65,  66,  67,  68,  69 
Roof  gardens,  66 
Roof  gardens  (illustration),  63 
Roof  gutters,  68,  69,  70 
Roof  loads,  173 
Rubble  work  as  an  accessory  (illustration), 

35 


Safe  loads  on  columns,  168 

Salt,  protection  from  freezing  by,  117 

Sand,  85 

Sand  blasting,  126 

Sand  blasting  (illustration),  128 

Sanitary  construction  (illustration),  138 

Scrubbed  surfaces,  126 

Seashore  house  of  concrete  (illustrations), 
14,  87 

Secondary  reinforcement,  141 

Sectional  forms,  77 

Sectional  wall  forms,  103 

Securing  reinforcement,  115 

Selected  aggregates,  129 

Selected  and  displayed  aggregates  (illus- 
trations), 131,  161 

Selection  and  care  of  steel  reinforcement, 
in 

Selection  of  materials,  85 

Separately  cast  details   (illustrations),  41, 

42,43 
Separately  cast  ornament,  44 


Separately  molded  members  (illustration), 
84 

Shingles,  67 

Shrinkage  rods  and  bars,  141 

Sills,  74,  75 

Simplicity,  27 

Simplicity  in  design  (illustrations),  31,  37, 
40 

Single  story  construction  (illustration),  22 

Slab  reinforcement,  185 

Slabs  and  beams  (illustrations),  55,  84 

Sloping  roofs,  67 

Small  houses  (illustrations),  22,  29,  120, 
181 

Solid  walls  (illustration),  87 

Sound-proof  properties,  15 

Spacers  for  reinforcement,  99 

Spading  concrete,  123 

Stairways,  52 

Stairways  (illustrations),  51,  84 

Standard  specifications  for  Portland  ce- 
ment, 85 

Steel  forms,  106 

Steps  (illustration),  71 

Stirrups,  59,  61,  187 

Stone,  86 

Strength  of  concrete,  147,  159,  164 

Strength  of  concrete  walls,  76 

Successful  use  of  concrete  (illustration),  35 

Surface  finish  (illustrations),  7,  14,  87. 
125,  127,  130,  131,  145,  153,  161 

Surface  treatment,  122  to  136  inclusive 


Tables   for  designing   reinforcement,    191 

to  197  inclusive 
Tamping  concrete,  124 
T-beams,  157,  158,  163,  164 
Terra  cotta  tile,  56,  57 
Texture — smooth  and  rough  (illustrations), 

48,  49.  50 
Tile  for  mosaic  inlay  (illustration),  45 
Tile  roofing,  67 
Tile,  their  use  as  a  decorative  medium. 

42.  134 

Timber  combined  with  concrete,  44 

Timber    combined    with    concrete    (illus- 
tration), 47 

Tooled  surfaces,  124,  129 

Top  coat  for  floors,  61 

Treatment  of  concrete  surfaces,  122 

Tying  reinforcement,  118 

Tying  and  separating  sides  of  forms,  100 

Types  of  floor  construction,  55 


Undercut    design    in    ornament    (illustra- 
tions), 41.  42,  43 
I  nit  panel  construction,  94,  95 


[  223  ] 


Untreated  exterior  surfaces,  123 
Untreated  surfaces  (illustrations),  14,  87, 

153.  188 
Up-keep,  low  cost  of  (illustration),  64 


Veneered,  lined  and  furred  walls,  81 
Vermin-proof  qualities,  15 
Vertical  column  reinforcement,  167 


Wall  construction,  75, 

Wall  forms,  77 

Walls  (illustration),  87 


76,  77,  78.  80,  81 


Water,  86 

Waterproof  joints,  73 

Waterproof  qualities  of  concrete  (illustra- 
tion), 72 

Weatherproof  concrete,  76 

Welded  frames,  60,  61 

Window  construction,  70,  73 

Window  and  door  frame  construction,  70, 
73.  74 

Wire  form  ties,  100 

Wiring  reinforcement,  118 

Wooden  floor  covering,  62 

Workingman's  cottage  (illustration),  10 

Working  stresses,  147 

Woven  wire,  59,  114 


[224] 


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